Overnight Ham and Swiss Breakfast Strata

Name: Overnight Ham and Swiss Breakfast Strata
Prep time: 15 min
Cook time: 1 h 10 min
Total time: 9 h 55 min
Yield: 8 servings
Cuisine: French
Ingredients: 2 tablespoons unsalted butter; 1 large yellow onion, about 12 ounces, halved and thinly sliced; 1/4 teaspoon kosher salt; 1 tablespoon unsalted butter, softened, for greasing the baking dish; 12 ounces day-old crusty country bread, sourdough, or French bread, cut into 1-inch cubes, about 10 cups; 12 ounces smoked ham, cut into 1/2-inch pieces; 8 ounces Swiss cheese, shredded, about 2 cups; 8 large eggs; 3 cups whole milk; 2 tablespoons Dijon mustard; 1 tablespoon finely chopped fresh thyme leaves; 2 tablespoons finely chopped fresh chives, plus additional chives for serving; 1 teaspoon kosher salt; 1/2 teaspoon freshly ground black pepper; 1/8 teaspoon ground nutmeg

Imperial August 8, 2026August 8, 2026

Quick Recipe Version (TL;DR)

Yield: 8 servings
Prep Time: 15 minutes
Cook Time: 1 hour 10 minutes
Total Time: 9 hours 55 minutes, including 8 hours chilling and 10 minutes resting

Quick Ingredients

3 tablespoons unsalted butter, divided
1 large yellow onion, thinly sliced
1 1/4 teaspoons kosher salt, divided
12 ounces day-old crusty bread, cut into 1-inch cubes
12 ounces smoked ham, diced
8 ounces Swiss cheese, shredded
8 large eggs
3 cups whole milk
2 tablespoons Dijon mustard
1 tablespoon chopped fresh thyme
2 tablespoons chopped fresh chives, plus more for serving
1/2 teaspoon freshly ground black pepper
1/8 teaspoon ground nutmeg

Do This

1. Butter a 9-by-13-inch baking dish and spread half of the bread in the bottom.
2. Cook the sliced onion in butter with salt for 20 minutes, until deeply golden and soft.
3. Layer the bread with the ham, Swiss cheese, caramelized onion, and remaining bread.
4. Whisk the eggs, milk, Dijon, herbs, pepper, nutmeg, and remaining salt; pour evenly over the layers.
5. Cover, refrigerate for 8 hours or overnight, and then let stand at room temperature for 20 minutes.
6. Bake at 350°F (175°C) for 30 minutes covered and 20 minutes uncovered; rest for 10 minutes before serving.

Why You’ll Love This Recipe

It is assembled the night before, making breakfast or brunch wonderfully low-stress.
Caramelized onions, smoky ham, nutty Swiss cheese, and Dijon give every layer plenty of savory flavor.
The bread absorbs the egg custard overnight, creating a tender center with a golden, lightly crisp top.
One generous casserole serves eight and pairs easily with fruit, salad, or roasted breakfast potatoes.

Grocery List

Produce: 1 large yellow onion, 1 small bunch fresh thyme, and 1 small bunch fresh chives
Dairy: 3 tablespoons unsalted butter, 8 large eggs, 3 cups whole milk, and 8 ounces Swiss cheese
Meat: 12 ounces smoked ham
Bakery: 1 small loaf crusty country bread, sourdough, or French bread, at least 12 ounces
Pantry: Dijon mustard, kosher salt, black pepper, and ground nutmeg

Full Ingredients

For the Caramelized Onion

2 tablespoons unsalted butter
1 large yellow onion, about 12 ounces, halved and thinly sliced
1/4 teaspoon kosher salt

For the Bread, Ham, and Cheese Layers

1 tablespoon unsalted butter, softened, for greasing the baking dish
12 ounces day-old crusty country bread, sourdough, or French bread, cut into 1-inch cubes, about 10 cups
12 ounces smoked ham, cut into 1/2-inch pieces
8 ounces Swiss cheese, shredded, about 2 cups

For the Egg Custard

8 large eggs
3 cups whole milk
2 tablespoons Dijon mustard
1 tablespoon finely chopped fresh thyme leaves
2 tablespoons finely chopped fresh chives, plus additional chives for serving
1 teaspoon kosher salt
1/2 teaspoon freshly ground black pepper
1/8 teaspoon ground nutmeg

Overnight Ham and Swiss Breakfast Strata – Closeup

Step-by-Step Instructions

Step 1: Prepare the baking dish and bread

Coat the bottom and sides of a 9-by-13-inch baking dish with 1 tablespoon of softened butter. Cut the day-old bread into roughly 1-inch cubes. Slightly dry bread is ideal because it absorbs the custard without becoming mushy. Spread half of the bread cubes in an even layer in the prepared dish.

Step 2: Caramelize the onion

Melt the remaining 2 tablespoons of butter in a large skillet over medium heat. Add the sliced onion and 1/4 teaspoon kosher salt. Cook for 5 minutes, stirring frequently, until the onion begins to soften. Reduce the heat to medium-low and continue cooking for 15 minutes, stirring every few minutes, until the onion is soft, sweet, and deep golden brown. Remove the skillet from the heat and let the onion cool for about 5 minutes.

Step 3: Build the savory layers

Scatter half of the diced ham, half of the shredded Swiss cheese, and all of the caramelized onion over the bread in the baking dish. Add the remaining bread, followed by the remaining ham and Swiss cheese. Distribute each ingredient evenly so every serving contains bread, ham, onion, and melted cheese.

Step 4: Mix and add the custard

In a large mixing bowl, whisk the eggs until the yolks and whites are completely blended. Add the whole milk, Dijon mustard, thyme, chives, 1 teaspoon kosher salt, black pepper, and nutmeg. Whisk until smooth and evenly combined. Slowly pour the custard over the casserole, moving around the dish so all of the bread is moistened.

Gently press the bread down with the back of a spoon or clean hands to help it absorb the custard. Avoid compacting the layers too firmly; the bread should remain loosely arranged so the finished strata has a light, custardy texture.

Step 5: Cover and refrigerate overnight

Cover the baking dish tightly and refrigerate for at least 8 hours or up to 24 hours. This resting time allows the bread to absorb the seasoned egg mixture and lets the flavors of the ham, Swiss cheese, Dijon, onions, and herbs blend together.

Step 6: Bake until golden and set

Remove the strata from the refrigerator and let it stand at room temperature for 20 minutes while the oven preheats to 350°F (175°C). Keep the dish covered and bake it on the center oven rack for 30 minutes. Carefully uncover the dish and bake for exactly 20 minutes more, until the top is golden, the cheese is bubbling, and the center is set. An instant-read thermometer inserted into the center should register at least 160°F (71°C).

Step 7: Rest, garnish, and serve

Place the baked strata on a heat-safe surface and let it rest for 10 minutes. Resting helps the custard finish setting and makes the casserole easier to cut into neat portions. Garnish with additional chopped chives, then cut into 8 squares and serve warm.

Pro Tips

Start with dry bread: Day-old bread absorbs the custard best. If your bread is fresh, spread the cubes on a baking sheet and dry them in a 300°F (150°C) oven for 10 minutes, then cool completely before assembling.
Shred the cheese yourself: Freshly shredded Swiss melts more smoothly than packaged shredded cheese, which may contain anti-caking starch.
Caramelize patiently: Keep the onion over medium-low heat after it softens. High heat can brown the edges before the center becomes sweet and tender.
Protect a glass dish: Let a refrigerated glass baking dish stand at room temperature as directed before placing it in the hot oven to reduce the risk of thermal shock.
Check the center: The outer edges set first. Test the middle of the strata for doneness; it should look moist but not liquid or jiggly.

Variations

Turkey and Gruyère: Replace the ham with 12 ounces diced smoked turkey and substitute an equal amount of shredded Gruyère for the Swiss cheese.
Spinach and mushroom: For a meatless version, replace the ham with 8 ounces sliced mushrooms and 5 ounces baby spinach. Sauté both until their released moisture has evaporated, then cool before layering.
Ham and asparagus: Add 1 cup of chopped, blanched asparagus to the layers for a fresh spring variation. Pat the asparagus dry before adding it to the casserole.

Storage & Make-Ahead

Assemble and refrigerate the unbaked strata for 8 to 24 hours before baking. Once baked, cool leftovers within 2 hours, cover them tightly, and refrigerate for up to 4 days. Reheat individual portions in the microwave for 60 to 90 seconds, or place several portions in a covered baking dish and warm at 325°F (165°C) for 15 to 20 minutes. Baked portions may also be wrapped individually and frozen for up to 2 months. Thaw them overnight in the refrigerator before reheating. For the best custardy texture, freezing the assembled but unbaked strata is not recommended.

Nutrition (per serving)