3 cups diced bread
4 large eggs
1 egg yolk
1 cup heavy cream (or half and half/more whole milk)
1/2 cup whole milk
4 ounces chevre, finely crumbled
3 ounces prosciutto, diced
1 teaspoon fresh thyme
2 shallot, minced
4 crimini mushrooms, sliced
Cracked pepper, to taste
1/4 cup shredded gruyere or parmesan (optional)

These rules are more like guidelines: try arugula, squash, arugula, peas, ricotta, sundried tomatoes, or whatever else strikes your fancy