Large Family Spinach and Cheese Strata

2 (10-ounce) packages frozen chopped spinach, thawed and squeezed dry 

2 large onions, finely chopped 

6 tablespoons unsalted butter 2 teaspoon salt, divided 

1 teaspoon black pepper, divided 

½ teaspoon ground nutmeg 

 2 loaves (16 cups) cubed French bread 

4 cups Italian cheese blend 

5 ½ cups milk 

18 large eggs 

4 tablespoons Dijon mustard 

 Prepare two 9×13 casserole dishes with nonstick cooking spray. In a large skillet over medium heat, saute the onions in butter, cooking until the onions are transparent and stirring as needed. Stir in 1 teaspoon of salt, ½ teaspoon of black pepper, and nutmeg and cook for an additional minute. Add the spinach, mixing until evenly distributed. In a large bowl, toss together the bread and spinach mixture. Divide the combination between the two casserole dishes. Sprinkle two cups of cheese blend over each casserole dish. Whisk together the milk, eggs, mustard, and remaining salt and pepper. Divide evenly between the two 9×13 greased casserole dishes, pouring over the top over the cheese. Cover and place in the refrigerator overnight or wrap well and freeze. When ready to bake: If frozen, thaw the strata in the refrigerator. Remove the casseroles from the refrigerator and allow to sit at room temperature for 30 minutes prior to baking. Preheat the oven to 350 degrees. Uncover and bake for 45 to 55 minutes. Let rest for 5 minutes before serving.

Source: Large Family Table