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egg spinach mushroom casserole

Egg Spinach Mushroom Casserole

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Prep Time 15 minutes
Cook Time 35 minutes
Resting Time 10 minutes
Total Time 1 hour
Course Breakfast
Cuisine American
Servings 6 servings

Equipment

  • 1 9x13 inch baking dish
  • 1 large skillet
  • 1 medium mixing bowl
  • 1 large mixing bowl
  • 1 Whisk
  • 1 Cutting board
  • 1 Chef's knife
  • 1 Wooden spoon
  • 1 measuring cup
  • 4 Measuring spoons
  • 1 Oven mitt
  • 1 Cooling rack or trivet

Ingredients
  

  • 1 tablespoon olive oil
  • 1 tablespoon unsalted butter
  • 1 medium yellow onion diced
  • 3 clove garlic minced
  • 8 ounce cremini mushrooms sliced
  • 6 ounce fresh spinach roughly chopped
  • 10 large eggs
  • 1 cup whole milk
  • 1/2 cup heavy cream
  • 1 cup shredded cheddar cheese
  • 1/2 cup grated Parmesan cheese
  • 1 teaspoon kosher salt
  • 1/2 teaspoon black pepper
  • 1/2 teaspoon smoked paprika
  • 1/4 teaspoon crushed red pepper flakes optional
  • 2 tablespoon fresh parsley chopped
  • 1 tablespoon fresh chives chopped
  • 1 tablespoon olive oil for greasing

Instructions
 

  • Preheat the oven to 375°F (190°C) and lightly grease a 9x13-inch baking dish with olive oil.
  • Heat olive oil and butter in a large skillet over medium heat until the butter melts and foams.
  • Sauté the diced onion for 3 to 4 minutes until translucent.
  • Add the garlic and cook for 30 seconds until fragrant.
  • Stir in the sliced mushrooms and cook for 6 to 8 minutes until they release moisture and brown.
  • Add the chopped spinach and cook for 1 to 2 minutes until just wilted, then remove the pan from heat.
  • In a large mixing bowl whisk together eggs, milk, and heavy cream until smooth.
  • Whisk in kosher salt, black pepper, smoked paprika, and crushed red pepper flakes if using.
  • Fold in cheddar, Parmesan, parsley, and chives.
  • Spread the mushroom and spinach mixture evenly in the prepared baking dish.
  • Pour the egg mixture over the vegetables, gently smoothing to distribute ingredients.
  • Bake for 28 to 35 minutes until the center is set and a knife inserted near the middle comes out clean.
  • Remove from the oven and let the casserole rest for 10 minutes to set before slicing.
  • Slice into squares and serve warm.

Notes

For best texture, avoid overcooking—pull the casserole when the center is just set with a slight jiggle, as it will continue to firm while resting. If you prefer a richer casserole, replace the milk with half-and-half or add an extra 1/2 cup of cheese. Make it ahead by assembling up to step 11, covering, and refrigerating overnight; bake an extra 5 to 10 minutes from cold. Drain or cook off mushroom moisture thoroughly to prevent a watery casserole. Add-ins like cooked bacon, sausage, or roasted red peppers work well, and you can substitute kale for spinach with a few extra minutes of sautéing. Let leftovers cool completely before refrigerating and reheat gently at 325°F to preserve moisture.
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