Easy Vegetarian Make-Ahead Breakfast Casserole

This wonderfully savory make-ahead breakfast casserole is brimming with vegetables. It’s perfect to feed a crowd on Christmas morning or at a festive brunch.

Tip

You can prepare this dish a day in advance, store it in the fridge, and bake it in the morning. It serves a happy crowd and is one of our favorite savory holiday breakfasts.

Breakfast casserole deep thoughts

I won’t bury the lede. We’ve become obsessed with this casserole. It all started with some leftover stuffing cubes from Thanksgiving. The really good kind where Whole Foods dries out all their little bits of leftover bakery bread, from sourdough to pumpernickel, and hands it to you in a bag that lasts approximately forever (like definitely until — not asking questions).

We’re not inherently a casserole family. I feel about 40 years too young and altogether not midwestern enough to aspire to something like that. It’s not that we don’t like family-style dishes baked lovingly in the oven and served alongside a simple green salad. We TOTALLY like that kind of food. Speaking for myself, I probably like it a little too much from time to time.

But when I hear the word “casserole,” I think of someone else. I don’t know — deep food thoughts for the day. 

And yet. Here we are with this happy-making CASSEROLE. (I might call it Breakfast Strata in private, okay?) It’s brimming with vegetables — onion, shiitakes, Christmas-colored peppers and broccoli. It’s super-savory. It’s pretty good for ya, considering. And it tastes SO good.

I can think of two scenarios where this dish would be the answer to your wildest dreams. (No presh, Umami Girl.) First: Christmas morning, or any morning when you have sleepover guests and don’t feel like cooking breakfast to order. You can make this dish a whole day in advance and take it out of the fridge when you wake up in the morning. It bakes in 40 minutes, during which time you’re free to be doing absolutely whatever else you like.
 
Second: this would be a fabulous anchor point for a festive and casual brunch, any time of year but especially around the holidays. Here’s what I would do:
 

Make-ahead breakfast casserole scenarios

I can think of two scenarios where this dish would be the answer to your wildest dreams. (No presh, Umami Girl.) First: Christmas morning, or any morning when you have sleepover guests and don’t feel like cooking breakfast to order. You can make this dish a whole day in advance and take it out of the fridge when you wake up in the morning. It bakes in 40 minutes, during which time you’re free to be doing absolutely whatever else you like.

Second: this would be a fabulous anchor point for a festive and casual brunch, any time of year but especially around the holidays.

Easy Vegetarian Make-Ahead Breakfast Casserole

I like to use my 5-quart braiser for this dish, because it can go from stovetop to oven. If you don’t have one of those, you can do the stovetop part in a 12-inch skillet and the baking part in any 5-quart baking dish. You can prepare this casserole the day before, store it tightly covered in the fridge and bake it the next morning. Remove from fridge about an hour before baking if possible, otherwise it may need to bake a little longer.
Prep Time 30 minutes
Cook Time 40 minutes
Total Time 1 hour 10 minutes
Serves Serves 10

Ingredients

  • 4 tablespoons butter
  • 1 medium yellow onion, diced
  • 1 green bell pepper, diced
  • 1 red bell pepper, diced
  • 10 ounces sliced shiitakes
  • 1 teaspoon salt, divided
  • 10 ounces frozen chopped broccoli, defrosted
  • 10 large eggs
  • 3 cups whole milk
  • 1/8 teaspoon nutmeg
  • Pinch ground cayenne
  • Freshly ground black pepper
  • 8 cups unseasoned dry stuffing cubes/bread cubes
  • 5 ounces shredded gruyere, divided
  • 4 tablespoons grated parmesan or pecorino, divided

Directions

  1. Melt the butter in the braiser or skillet over medium-high heat. Add the onion, peppers, and shiitakes all at once, along with 1/2 teaspoon of the salt. Cook, stirring from time to time, for about 10 minutes, until the vegetables have softened, browned a bit, and decreased in volume by at least half. Remove from heat.
  2. While the other vegetables cook, place the defrosted broccoli on a thick layer of paper towels and cover with another thick layer. When the veggies in the skillet have cooked as noted above, press down gently on the paper towels to remove moisture from the broccoli. The add broccoli to the skillet and stir to incorporate.
  3. Crack the eggs into a large mixing bowl and beat well with a fork. Stir in milk, nutmeg, cayenne, and a few good grinds black pepper. Add bread cubes and stir to moisten. Then stir in all the vegetables, half the gruyere and half the parmesan or pecorino. Pour the whole mixture back into the braiser or into the baking pan and sprinkle with the remaining cheese. Cover and refrigerate overnight or for at least a few hours before proceeding. Remove from fridge about an hour before baking if possible.
  4. An hour before serving time, preheat oven to 375°F with a rack in the center. Bake uncovered for about 40 minutes, until puffed and golden. Serve hot or even at room temperature.

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