Cheesy Spinach and Mushroom Breakfast Stuffing

published Apr 2, 2023
Cheesy Spinach and Mushroom Breakfast Stuffing Recipe

A cheesy egg-free breakfast casserole with spinach and mushrooms.

Serves8 to 10

Prep30 minutes

Cook1 hour

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eggless strata in baking pan with scoop out and some on spoon
Credit: Photo: Lucy Schaeffer; Food Styling: Jessie YuChen

Recently, when egg prices soared and availability plummeted, the workhorse of the cooking and baking world became a precious commodity. I started thinking about the large number of eggs that are used in breakfast casseroles and wondered if it would be possible to make them without eggs. Baking without eggs is not an easy task, but it’s not an impossible one. Borrowing a page from Thanksgiving stuffing or dressing, I used broth to both moisten the bread and add flavor to this savory breakfast casserole — and it worked wonderfully well. 

Whether you’re trying to eat egg-free or just want to skip buying as many eggs, this breakfast stuffing — inspired by the flavors of a cheese, spinach, and mushroom quiche — bakes into a satisfying breakfast that serves a crowd. But hey, if you also want to serve this during the holidays as a side dish, be my guest!

What Is Breakfast Stuffing?

This breakfast stuffing reminds me of one of my favorite dishes my mother used to make: A cheesy quiche loaded with spinach and mushrooms. Here, I sauté onion, spinach, and cremini mushrooms together, and then toss them together with toasted bread cubes. The addition of shredded Swiss cheese takes this into cheesy breakfast territory, but just like a Thanksgiving stuffing, everything is mixed together with broth rather than a custard made with eggs and milk. Transfer to a baking dish, sprinkle with more cheese, and bake until golden-brown.

Breakfast stuffing has all the flavors of a quiche, but with bread standing in for the pie crust. If you like the custard that holds traditional breakfast casseroles together, I recommend scooping from the center of the stuffing when serving, but if you’re a fan of crispy bits of bread and cheese, go for the edges of the casserole instead.

Credit: Photo: Lucy Schaeffer; Food Styling: Jessie YuChen

Ingredients You’ll Need for Breakfast Stuffing

  • Crusty bread: French or Italian bread work great here. I tested with sourdough bread, but I didn’t care much for its sour flavor, which really comes through, especially since there’s no eggy custard to cut through it.
  • Veggies: You’ll need a yellow onion, a pound of cremini mushrooms, and a bag of baby spinach.
  • Thyme: Dried thyme partners really well with the spinach and mushrooms.
  • Cheese: Swiss cheese is lovely here, but a Gruyère or Comté would also be great.
  • Broth: You’ll moisten the stuffing with chicken or vegetable broth.

How to Make Breakfast Stuffing Ahead of Time

I’m not at my sharpest first thing in the morning, so any part of breakfast I can pre-make is welcome in my book. For this breakfast stuffing, toast the bread and sauté the vegetables the night before, but stop at the point where you would add the broth. Toss the bread, veggies, and half of the cheese together in the bowl, then cover and refrigerate. Skipping the broth at this point will prevent the bread from becoming too soggy as it sits overnight. 

When you’re ready to bake, stir in the broth, toss again, then continue with the instructions for assembling and baking. The stuffing may need a few more minutes of baking time.

Cheesy Spinach and Mushroom Breakfast Stuffing Recipe

A cheesy egg-free breakfast casserole with spinach and mushrooms.

Prep time 30 minutes

Cook time 1 hour

Serves 8 to 10

Nutritional Info

Ingredients

  • 1 (16- to 18-ounce) loaf

    unsliced French or Italian bread

  • Cooking spray or butter, for the baking dish

  • 1 pound

    cremini mushrooms

  • 1

    medium yellow onion

  • 1 teaspoon

    dried thyme

  • 1 1/4 teaspoons

    kosher salt, divided, plus more as needed

  • 1/4 teaspoon

    freshly ground black pepper, plus more as needed

  • 4 tablespoons

    (1/2 stick) unsalted butter

  • 8 ounces

    Swiss cheese, shredded (about 2 cups)

  • 1 (5 to 6-ounce) bag

    baby spinach (5 to 6 packed cups)

  • 1 1/2 cups

    low-sodium vegetable or chicken broth

Instructions

  1. Cut or tear 1 (16- to 18-ounce) loaf French or Italian bread into rough 1-inch pieces (10 to 12 cups). Arrange in an even layer on a rimmed baking sheet. Dry out the bread by either leaving it uncovered at room temperature overnight, or baking it in a 250ºF oven until just starting to dry out but not browned, 10 to 12 minutes.

  2. Arrange a rack in the middle of the oven and heat the oven to 375ºF. Meanwhile, coat a 9x13-inch or other 3-quart baking dish with cooking spray or butter. Trim and slice 1 pound cremini mushrooms about 1/4-inch thick (about 6 cups). Dice 1 medium yellow onion (about 1 1/2 cups).

  3. Melt 4 tablespoons unsalted butter in a large frying pan over medium-high heat. Add the mushrooms, onion, 1 teaspoon dried thyme, 3/4 teaspoon of the kosher salt, and 1/4 teaspoon black pepper. Cook, stirring occasionally, until the mushrooms are browned and the onion is softened, and the moisture in the pan is evaporated, 8 to 10 minutes. Meanwhile, grate 8 ounces Swiss cheese on the large holes of a box grater (about 2 cups).

  4. Add 5 to 6 ounces baby spinach to the pan a few handfuls at a time, stirring between each addition. Cook, stirring occasionally, until the spinach is wilted. Add 1 1/2 cups low-sodium broth and the remaining 1/2 teaspoon kosher salt. Scrape up any browned bits from the bottom of the pan and bring the broth to a simmer.

  5. Transfer to a large bowl. Add the bread and half of the cheese. Toss until evenly moistened. Taste and season with more kosher salt and black pepper as needed. Transfer to the baking dish and spread into an even layer. Sprinkle with the remaining cheese.

  6. Bake until the top is golden brown in spots, 35 to 40 minutes.

Recipe Notes

Make ahead: The stuffing can be made up to 1 day ahead without the chicken broth. Toss the bread cubes, cooked spinach and mushrooms, and half the cheese together in a large bowl, cover, and refrigerate. When ready to bake, stir in the broth, then transfer to the baking dish and sprinkle with the remaining cheese. Bake as directed, it may need a few more minutes of baking time.

Storage: Leftovers can be refrigerated in an airtight container for up to 4 days.