Preheat your oven to 375ºF and grease a 9x13 baking dish.
In a large bowl, whisk together the eggs, half-and-half, salt and pepper.
12 large eggs, 1 1/2 cups half-and-half, 1 teaspoon salt, 1/4 teaspoon ground black pepper
Rip up the croissants by hand, adding them to the egg mix bowl as you go. Try to rip them in pieces about 1-2 inches in size.
6 large croissants, baked
Stir in the chopped ham, onions, spinach and 1 cup of the shredded cheddar cheese.
1 pound chopped ham, 1 cup chopped onions, 2 cups baby spinach, 2 cups shredded cheddar cheese
Pour the mixture into the prepared casserole dish and sprinkle the top of the casserole with the remaining cheese.
Bake for 50 minutes. The casserole should be completely set in the center and not jiggle when touched. The top will be golden brown and all the cheese will be melted.
Slice and serve the casserole while warm.