Savory Leftover Bread Strata with Spinach and Onions

Why You’ll Love This Recipe

• Turns leftover bread into a cozy, puffy bake with crisp edges and a silky custard center.
• Caramelized onions and spinach add deep flavor and color without much fuss.
• Flexible: assemble ahead for brunch or bake same day for an easy dinner.
• Uses a modest amount of cheese for savoriness without heaviness.

Grocery List

• Produce: 2 large yellow onions, 2 cloves garlic, optional fresh thyme, optional parsley or chives for garnish
• Dairy: Whole milk, unsalted butter, eggs, Gruyère or sharp cheddar, Parmesan
• Pantry: Stale bread, extra-virgin olive oil, Dijon mustard, ground nutmeg, kosher salt, black pepper, red pepper flakes (optional), balsamic vinegar (optional), frozen chopped spinach

Full Ingredients

Caramelized Onions & Spinach

• 2 large yellow onions (about 1 1/2 lb), thinly sliced
• 2 tbsp unsalted butter
• 1 tbsp extra-virgin olive oil
• 1/2 tsp kosher salt
• 2 cloves garlic, minced
• 1 tsp balsamic or sherry vinegar (optional, for deglazing)
• 1/2 tsp fresh thyme leaves or 1/4 tsp dried thyme (optional)
• 1/4 tsp red pepper flakes (optional)
• 10 oz frozen chopped spinach, thawed and squeezed very dry

Egg-Milk Custard

• 8 large eggs
• 2 3/4 cups whole milk
• 1 tsp Dijon mustard
• 1 tsp kosher salt
• 1/2 tsp freshly ground black pepper
• 1/4 tsp ground nutmeg

Bread & Cheese

• 10 cups stale crusty bread, cut into 1-inch cubes (about 10–12 oz)
• 1 cup (4 oz) shredded Gruyère or sharp cheddar
• 2 tbsp finely grated Parmesan, for topping
• 1 tbsp unsalted butter, for greasing the baking dish

Step-by-Step Instructions

Step 1: Prep the bread and pan

Butter a 9×13-inch baking dish. If your bread is fresh, spread the cubes on a sheet pan and bake at 300°F for 10–15 minutes to dry them slightly; cool 5 minutes. Dry bread soaks up custard better and bakes up with beautifully crisp edges.

Step 2: Slowly caramelize the onions

In a large skillet over medium-low heat, melt the butter with the olive oil. Add the onions and 1/2 tsp kosher salt. Cook, stirring every few minutes, until the onions are soft, deep golden, and jammy, about 25–30 minutes. If the pan looks dry or browned bits build up, splash in the optional balsamic to deglaze. Stir in the garlic for 1 minute. Add optional thyme and red pepper flakes; remove from heat.

Step 3: Dry out the spinach

Thaw the spinach completely and squeeze it very dry—wring it in a clean kitchen towel or several layers of paper towel until almost no liquid drips. Stir the spinach into the onions and cook 1–2 minutes over medium heat to evaporate any remaining moisture. Set aside to cool slightly.

Step 4: Whisk the custard

In a large bowl, whisk the eggs until evenly mixed. Whisk in the milk, Dijon, kosher salt, pepper, and nutmeg until smooth. This seasoned custard is the backbone of your strata—taste and adjust salt if your cheese is very salty.

Step 5: Layer it up

Scatter half the bread into the prepared dish. Top with half the onion–spinach mixture, then half the shredded cheese. Repeat with remaining bread, onion–spinach, and cheese. Slowly pour the custard evenly over everything, then use your hands or the back of a spatula to gently press the top so all the bread is moistened. Sprinkle Parmesan over the surface.

Step 6: Soak, then bake

Let the strata soak at room temperature for 20–30 minutes (or cover and refrigerate up to 12 hours). When ready to bake, preheat the oven to 350°F. If refrigerated, let the dish sit at room temperature while the oven heats. Bake on the middle rack until puffed, deeply golden, and the center is just set, 45–55 minutes. An instant-read thermometer inserted in the center should read about 165°F. Tent with foil if it browns too quickly.

Step 7: Rest, slice, and serve

Cool the strata for 10 minutes to let the custard settle. Cut into generous squares and serve warm. A shower of chopped parsley or chives is a nice fresh finish.

Pro Tips

• Squeeze the spinach until your hands get tired—excess moisture is the enemy of a custardy (not soggy) strata.
• Press the bread into the custard after pouring; a quick press ensures even soaking and an even rise.
• If using very salty cheese, reduce the custard salt to 3/4 tsp.
• Make-ahead magic: an overnight rest deepens flavor and yields an extra-tender interior; add 5–10 minutes to baking if very cold.
• Check doneness in the very center; look for a mild jiggle but no liquid pooling, or confirm 165°F with a thermometer.

Variations

• Mushroom–Swiss: Sauté 12 oz sliced cremini mushrooms until browned and add with the onions; use Swiss or Gruyère. Reduce spinach to 6 oz.
• Bacon–Cheddar: Cook 6 slices thick-cut bacon until crisp; crumble and layer with sharp cheddar. Reduce custard salt to 3/4 tsp.
• Tomato–Feta–Herb: Drain and pat dry 1 1/2 cups chopped tomatoes; layer with 3 oz crumbled feta and chopped basil or parsley. Add tomatoes on top layer to keep the bottom from getting soggy.

Storage & Make-Ahead

Refrigerate leftovers, tightly covered, for up to 4 days. Reheat covered at 350°F for 15–20 minutes, then uncover 3–5 minutes to crisp the top, or microwave individual squares 60–90 seconds. To make ahead, assemble and refrigerate up to 12 hours; bake as directed, adding 5–10 minutes if the center is still cool. To freeze, wrap baked, cooled squares individually and freeze up to 2 months; reheat from frozen at 325°F for 25–35 minutes or microwave in short bursts, then crisp under the broiler if desired.

Nutrition (per serving)

Approx. 350 calories; 17 g protein; 24 g carbohydrates; 20 g fat; 2 g saturated fat; 3 g fiber; 640 mg sodium. Values are estimates and will vary with brands and exact ingredients.