Quick Recipe Version (TL;DR)
Quick Ingredients
- 1 x 9-inch (23 cm) pie crust (homemade or store-bought), fitted into a pie dish
- 2 tbsp (28 g) unsalted butter
- 1 tbsp (15 ml) olive oil
- 2 lb (900 g) yellow onions, thinly sliced
- 1 tsp fine salt, divided
- 1/2 tsp black pepper
- 1 tsp fresh thyme leaves (or 1/2 tsp dried thyme)
- 1 tsp Dijon mustard
- 4 large eggs
- 1 cup (240 ml) heavy cream
- 1/2 cup (120 ml) whole milk
- 8 oz (225 g) sharp cheddar, grated
- 4 oz (115 g) extra-sharp cheddar, grated
Do This
- 1) Blind-bake crust at 375°F (190°C) for 20 minutes (with weights), then 10 minutes uncovered.
- 2) Sauté onions in butter + oil with 1/2 tsp salt until deeply soft and golden, 18–22 minutes; cool 10 minutes.
- 3) Whisk eggs, cream, milk, Dijon, remaining 1/2 tsp salt, pepper, and thyme.
- 4) Sprinkle half the cheese into warm crust; add onions; top with remaining cheese.
- 5) Pour egg mixture over filling; tap dish to settle.
- 6) Bake at 350°F (175°C) until just set, 35–45 minutes; rest 15 minutes before slicing.
Why You’ll Love This Recipe
- Deeply savory-sweet onions with sharp cheddar for classic comfort flavor.
- A creamy, custardy egg base that slices cleanly but stays tender.
- Great warm, room temp, or cold, making it ideal for lunches and picnics.
- Uses simple grocery-store ingredients with big, cozy payoff.
Grocery List
- Produce: Yellow onions (about 2 lb / 900 g), fresh thyme (optional)
- Dairy: Unsalted butter, sharp cheddar, extra-sharp cheddar, heavy cream, whole milk, eggs
- Pantry: Olive oil, Dijon mustard, fine salt, black pepper, pie crust (or ingredients to make one)
Full Ingredients
For the crust
- 1 x 9-inch (23 cm) unbaked pie crust, fitted into a 9-inch (23 cm) pie dish and crimped (store-bought refrigerated crust is fine)
- Pie weights or dried beans/rice for blind baking
For the sautéed onion filling
- 2 tbsp (28 g) unsalted butter
- 1 tbsp (15 ml) olive oil
- 2 lb (900 g) yellow onions (about 4 large), halved and thinly sliced
- 1 tsp fine salt, divided
- 1/2 tsp freshly ground black pepper
- 1 tsp fresh thyme leaves (or 1/2 tsp dried thyme)
For the creamy egg base
- 4 large eggs
- 1 cup (240 ml) heavy cream
- 1/2 cup (120 ml) whole milk
- 1 tsp Dijon mustard
Cheese
- 8 oz (225 g) sharp cheddar, grated (preferably white cheddar)
- 4 oz (115 g) extra-sharp cheddar, grated
Step-by-Step Instructions
Step 1: Prep the oven and crust
Place a rack in the lower-middle of the oven. Preheat to 375°F (190°C).
Fit your pie crust into a 9-inch (23 cm) pie dish, pressing it gently into the corners. Crimp the edge. Chill the crust in the refrigerator for 10 minutes (this helps prevent shrinkage during baking).
Step 2: Blind-bake the crust for a crisp base
Line the chilled crust with parchment paper and fill with pie weights (or dried beans/rice), making sure the weights go up the sides.
Bake at 375°F (190°C) for 20 minutes. Carefully lift out the parchment and weights, then bake the crust uncovered for 10 minutes, until the bottom looks dry and lightly golden.
Reduce the oven temperature to 350°F (175°C). Leave the crust on a baking sheet (this makes it easier to move and catches any drips).
Step 3: Slowly sauté the onions until sweet and golden
While the crust bakes, warm a large skillet over medium heat. Add the butter (2 tbsp / 28 g) and olive oil (1 tbsp / 15 ml).
Add the sliced onions and sprinkle with 1/2 tsp of the salt. Cook, stirring every few minutes, until the onions are very soft, reduced in volume, and golden with some deeper caramel-colored edges, 18–22 minutes.
Stir in the black pepper and thyme. Transfer onions to a plate or bowl and let cool for 10 minutes so they don’t overcook the custard.
Step 4: Whisk the creamy egg base
In a medium bowl, whisk together the eggs, heavy cream, whole milk, Dijon mustard, and the remaining 1/2 tsp salt until smooth and well combined.
If you want an extra-silky texture, let the mixture sit for 5 minutes so bubbles rise and pop.
Step 5: Layer cheese and onions into the crust
Sprinkle half of the grated cheddar mixture into the warm par-baked crust (this creates a little “cheese barrier” that helps keep the bottom crisp).
Spoon the cooled sautéed onions evenly over the cheese. Scatter the remaining cheese over the top.
Step 6: Add custard and bake until just set
Place the pie (on its baking sheet) on the oven rack. Slowly pour the egg mixture over the filling. If needed, pause to let it settle into the onions, then continue until all custard is added.
Bake at 350°F (175°C) for 35–45 minutes, until the center is just set. The pie is done when the edges are set and the middle gives a gentle wobble (not a wet slosh). An instant-read thermometer inserted near the center should read about 165°F (74°C).
If the crust edge browns too quickly, cover it with a pie shield or strips of foil during the last 10–15 minutes.
Step 7: Rest, slice, and serve
Let the pie rest on a cooling rack for 15 minutes before slicing. This helps the custard fully set so you get clean wedges.
Serve warm or at room temperature. It’s wonderful with a simple green salad, pickles, or a spoonful of chutney.
Pro Tips
- Go low and slow on the onions: Rushing them can leave sharp onion bite. Aim for soft, jammy onions with a golden hue.
- Grate your own cheese: Pre-shredded cheese often contains anti-caking agents that can make the filling less creamy.
- Don’t overbake: The pie should still have a slight wobble in the center when it comes out; it will continue setting as it rests.
- Keep the crust crisp: Blind-baking plus that first layer of cheese helps prevent a soggy bottom.
- Use a baking sheet: It stabilizes the pie and makes it much easier to move in and out of the oven.
Variations
- Cheese & onion with leek: Replace 1 lb (450 g) of the onions with sliced leeks (well washed). Cook until very soft.
- Mustard and chive boost: Add 2 tbsp chopped chives to the custard and increase Dijon to 2 tsp.
- Crust swap: Use puff pastry for a lighter, flaky base; blind-bake it the same way, watching closely for faster browning.
Storage & Make-Ahead
Cool leftovers completely, then refrigerate tightly covered for up to 4 days. Reheat slices on a baking sheet at 325°F (165°C) for 12–15 minutes (this helps re-crisp the crust), or microwave gently for 45–75 seconds (softer crust).
To make ahead: you can blind-bake the crust up to 1 day in advance (cool, cover, and store at room temperature), and sauté the onions up to 2 days ahead (refrigerate). Assemble and bake the day you want to serve for the best texture.
Nutrition (per serving)
Approximate, based on 8 slices: 470 calories, 31 g fat, 29 g carbs, 18 g protein, 2 g fiber, 680 mg sodium.
