Spinach Mushroom Strata

• frozen spinach, thawed↗5 ounces
• unsalted butter↗2 tablespoons
• finely chopped onion (1 medium)1 cup
• chopped mushrooms5 ounces
• salt (divided)↗1 teaspoon
• black pepper↗1⁄2 teaspoon
• freshly grated nutmeg1⁄4 teaspoon
• whole wheat bread, cubed (1 inch)↗4 cups
• coarsely grated gruyere (1 cup)3 ounces
• finely grated parmesan cheese (1/2 cup)1 ounce
• milk↗1 1⁄2 cups
• large eggs↗4
• Dijon mustard↗1 tablespoon

Step-by-step instructions

1. 1

   Squeeze liquid from spinach and set aside.

2. 2

   Heat butter over medium heat and cook onion and mushrooms until soft.

3. 3

   Add 1/2 teaspoon of the salt and the pepper and nutmeg and cook for one minute.

4. 4

   And spinach, stir, and remove from heat.

5. 5

   In a lightly buttered 1 1/2 to 2 quart casserole, spread one third of the bread cubes across the bottom, then 1/3 of the spinach mixture, then 1/3 of the Gruyere, and 1/3 of the Parmesan.

6. 6

   Continue layering ingredients, finishing with a cheese layer.

7. 7

   Whisk together the milk, eggs, and mustard. Pour evenly over casserole.

8. 8

   Bake at 350 degrees for about 45 minutes, until golden brown and puffy in the middle. Casserole can be refrigerated overnight before cooking.