Preheat the oven to 350° F.

In a bowl, whisk together the eggs, half and half, cheese, salt, and pepper.

Heat a large (10-inch) oven-safe skillet over medium heat, and add the butter. Add the leftover stuffing and cook until the bread cubes are toasted and golden, stirring often. Pour the egg mixture over the top. Swirl the spinach into the eggs.

Cook the frittata for 5 minutes, not stirring, until it's just set around the edges.

Place it in the oven and bake for 20 to 25 minutes. Remove and let cool slightly before serving. Slice into wedges and serve with extra parmesan cheese.