Caramelized Onion and Goat Cheese Tart with Thyme

Quick Recipe Version (TL;DR)

A crisp, buttery tart layered with deeply caramelized onions, tangy goat cheese, Dijon mustard, fresh thyme, and toasted walnuts. A little egg-and-cream custard brings everything together without overpowering the onions.

• Yield: 1 tart, 9 inches across; 8 servings
• Prep Time: 35 minutes
• Cook Time: 1 hour 30 minutes, with overlapping stovetop and oven cooking
• Total Time: 2 hours 30 minutes, including chilling and a 15-minute rest, with overlapping tasks

Quick Ingredients

• Pastry: 1⅓ cups (160 g) all-purpose flour, 6 tablespoons (85 g) cold unsalted butter, ¼ teaspoon fine sea salt, and 3 tablespoons (45 ml) ice water; plus 1 tablespoon (8 g) flour for rolling.
• Onions: 2 pounds (900 g) peeled yellow onions, thinly sliced; 1 tablespoon (15 ml) olive oil; 1 tablespoon (14 g) unsalted butter; ½ teaspoon fine sea salt; ¼ teaspoon black pepper; and 2 tablespoons (30 ml) water for deglazing if needed.
• Filling: 6 ounces (170 g) plain soft goat cheese, 2 large eggs, ⅓ cup (80 ml) heavy cream, and 1 tablespoon (15 g) Dijon mustard.
• Finishing touches: ⅓ cup (40 g) chopped walnuts and 1 tablespoon fresh thyme leaves, divided.

Do This

• 1. Rub the pastry butter into the flour and salt, mix in the ice water, form a disk, and refrigerate for 30 minutes.
• 2. Cook the onions in the oil and remaining butter for 50 minutes: 10 minutes over medium heat, then 40 minutes over medium-low. Stir in 2 teaspoons thyme during the final 2 minutes.
• 3. During the onion cooking time, heat the oven to 375°F (190°C). Roll the dough into a 12-inch circle, line a 9-inch tart pan, and chill for 10 minutes. Toast the walnuts for 5 minutes.
• 4. Line the pastry with parchment and pie weights. Bake for 20 minutes, remove the weights and parchment, and bake for 5 minutes more.
• 5. Lower the oven to 350°F (175°C). Brush Dijon over the shell, add the cooled onions, goat cheese, and walnuts, then pour over the eggs whisked with the cream.
• 6. Bake for 35 minutes, until golden and just set. Rest for 15 minutes and finish with the remaining 1 teaspoon thyme.

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Why You’ll Love This Recipe

• Holiday-worthy without being fussy: Golden pastry, creamy goat cheese, and fresh thyme make a lovely centerpiece.
• Beautifully balanced: Sweet onions meet tangy cheese, a gentle mustard kick, and crunchy toasted walnuts.
• A genuinely crisp base: Blind baking keeps the buttery pastry from turning soggy beneath the filling.
• Easy to plan ahead: Prepare the dough and onions in advance, then assemble and bake when you need it.

Grocery List

• Produce: Yellow onions, enough for 2 pounds (900 g) after peeling; 1 small bunch fresh thyme.
• Dairy: Unsalted butter, 7 tablespoons (99 g) total; plain soft goat cheese, 6 ounces (170 g); heavy cream, ⅓ cup (80 ml).
• Eggs: 2 large eggs.
• Pantry: All-purpose flour, olive oil, Dijon mustard, walnuts, fine sea salt, and black pepper.

Full Ingredients

For the Buttery Pastry

• 1⅓ cups (160 g) all-purpose flour
• ¼ teaspoon fine sea salt
• 6 tablespoons (85 g) cold unsalted butter, cut into ½-inch cubes
• 3 tablespoons (45 ml) ice water
• 1 tablespoon (8 g) all-purpose flour, for rolling

For the Caramelized Onions

• 2 pounds (900 g) peeled yellow onions, halved and sliced ⅛ inch thick from root to tip
• 1 tablespoon (15 ml) olive oil
• 1 tablespoon (14 g) unsalted butter
• ½ teaspoon fine sea salt
• ¼ teaspoon freshly ground black pepper
• 2 teaspoons fresh thyme leaves
• 2 tablespoons (30 ml) water, for deglazing if the pan becomes dry

For the Filling and Finish

• ⅓ cup (40 g) roughly chopped walnuts
• 1 tablespoon (15 g) Dijon mustard
• 6 ounces (170 g) plain soft goat cheese, broken into small pieces
• 2 large eggs
• ⅓ cup (80 ml) heavy cream
• 1 teaspoon fresh thyme leaves, for finishing

Equipment: A 9-inch-wide, 1-inch-deep tart pan with a removable bottom; a 12-inch heavy skillet; a rolling pin; parchment paper; pie weights or dried beans; and two baking sheets.

Step-by-Step Instructions

Step 1: Make and chill the pastry

Whisk the flour and salt together in a mixing bowl. Add the cold butter and rub it into the flour with your fingertips until the mixture resembles coarse breadcrumbs with a few pea-sized pieces of butter remaining. Keep your touch light so the butter stays cold.

Drizzle in the 3 tablespoons ice water and toss with a fork. Gently squeeze the mixture together into a dough without kneading. It should hold together when pressed. Flatten into a 1-inch-thick disk, wrap, and refrigerate for 30 minutes. Begin the onions while it chills.

Step 2: Slowly caramelize the onions

Heat the olive oil and 1 tablespoon butter in a 12-inch heavy skillet over medium heat. Add the sliced onions and salt. Cook for 10 minutes, stirring frequently, until the onions soften and begin to collapse.

Reduce the heat to medium-low and cook for another 40 minutes, stirring every 3 to 5 minutes and more frequently toward the end. Scrape the golden deposits from the bottom of the pan back into the onions. If those deposits start becoming very dark, add the measured water 1 tablespoon at a time, scraping as you stir, and let it evaporate.

During the final 2 minutes, stir in the black pepper and 2 teaspoons thyme. The finished onions should be deeply golden brown, soft, and jammy, with no watery liquid remaining. Remove from the heat and spread on a plate to cool until no longer steaming. Start the next step during the final 20 minutes of onion cooking.

Step 3: Shape the shell and toast the walnuts

Heat the oven to 375°F (190°C), with racks in the lower and upper thirds. Place a sturdy baking sheet on the lower rack to preheat. On a surface dusted with the rolling flour, roll the chilled pastry into a 12-inch circle, approximately ⅛ inch thick.

Ease the dough into the tart pan without stretching it. Press gently into the corners, trim the excess level with the rim, and prick the base lightly with a fork. Refrigerate the lined pan for 10 minutes.

Meanwhile, spread the walnuts on a separate baking sheet and toast on the upper rack for 5 minutes, stirring once halfway through. Transfer to a plate to cool. They should smell nutty and look lightly golden, not dark brown.

Step 4: Blind bake the pastry

Line the chilled pastry with crumpled parchment paper and fill with pie weights or dried beans, making sure the weights support the sides as well as the base. Set the tart pan on the hot lower baking sheet and bake for 20 minutes.

Carefully lift out the parchment and weights. Return the shell to the oven for 5 minutes, until the base looks dry and the edges are pale golden. Reduce the oven temperature to 350°F (175°C). Leave the hot baking sheet in place.

Step 5: Layer the filling

Whisk the eggs and cream together in a bowl until completely combined. Brush the Dijon mustard in a thin, even layer over the warm pastry base.

Spread the cooled onions evenly over the mustard without packing them tightly. Scatter over the goat cheese and toasted walnuts, distributing them all the way to the edges. Slowly pour the egg mixture into the spaces between the filling, keeping it below the pastry rim. Leave some goat cheese and walnuts visible on top.

Step 6: Bake until golden and just set

Return the tart to the hot baking sheet and bake at 350°F (175°C) for 35 minutes. The pastry should be golden, the exposed goat cheese lightly colored, and the filling set around the edges with only a slight wobble in the center. The center should reach 160°F (71°C) on an instant-read thermometer; if it has not, continue baking in 3-minute increments.

If the pastry edges or walnuts brown too quickly, cover the tart loosely with foil for the remainder of baking. Avoid baking until the center is completely firm, which can make the custard dry.

Step 7: Rest, garnish, and serve

Set the tart pan on a wire rack and rest for 15 minutes. Carefully remove the outer ring, then transfer the tart to a serving plate. Scatter over the remaining 1 teaspoon fresh thyme leaves and cut into 8 wedges.

Serve warm with a crisp green salad, roasted vegetables, or a simple holiday spread. The filling will slice more cleanly after resting, while the pastry will still have a lovely crisp bite.

Pro Tips

• Let the onions guide you: Fifty minutes is the cooking target, but skillet material and onion moisture affect browning. If they are still pale, keep cooking over medium-low heat until jammy and golden; do not turn up the heat to rush them.
• Keep the pastry relaxed: Chilling before rolling and again after lining the pan helps prevent shrinkage. Never stretch the dough into the corners.
• Cool the onions before filling: Hot, steaming onions can soften the shell and start cooking the egg mixture before the tart reaches the oven.
• Use soft goat cheese: A plain, fresh goat cheese log gives creamy pockets throughout the tart. Aged, firm goat cheese produces a different texture.
• Protect the crisp base: Blind bake until the bottom looks dry, and keep the tart on the preheated baking sheet for the final bake.

Variations

• Nut-free tart: Omit the walnuts. For a little crunch, replace them with ¼ cup (35 g) pumpkin seeds, toasted at 375°F (190°C) for 5 minutes.
• Different cheese: Replace the goat cheese with 6 ounces (170 g) crumbled feta for a saltier filling. Reduce the salt in the onions to ¼ teaspoon.
• Rosemary and thyme: Use 1 teaspoon finely chopped fresh rosemary and 1 teaspoon thyme in the onions, then keep the thyme garnish as written.

Storage & Make-Ahead

Make ahead: Refrigerate the wrapped pastry dough for up to 2 days, or freeze for up to 2 months and thaw overnight in the refrigerator. Let refrigerated dough sit at room temperature for 10 minutes before rolling if it is too firm. Cook the onions up to 3 days ahead, cool promptly, and refrigerate in an airtight container. Toast the walnuts up to 1 week ahead and keep airtight at room temperature. Assemble the tart shortly before its final bake.

Store: Refrigerate leftover tart, covered, within 2 hours of baking and keep for up to 4 days. Freeze individually wrapped, fully cooled slices for up to 2 months; thaw overnight in the refrigerator.

Reheat: Place refrigerated slices on a baking sheet in a 325°F (165°C) oven for 15 minutes, or until the center reaches 165°F (74°C). If needed, continue heating in 3-minute increments. Cover loosely with foil if the walnuts begin to darken. Oven reheating preserves the crust better than microwaving.

Nutrition (per serving)

Estimated for 1 of 8 servings, using the homemade pastry and all filling ingredients.

Calories: 370 kcal | Carbs: 28g | Protein: 10g | Fat: 25g | Saturated Fat: 13g | Fiber: 3g | Sugar: 6g | Sodium: 400mg | Cholesterol: 95mg