Heat oven to 350 degrees. and coat a 6-cupcake pan with a nonstick cooking spray. Whisk together the eggs, half and half, and salt in a medium bowl, then evenly distribute the egg mixture among the cup-cake pan. Add about 2 tablespoons of mix-ins to each cup, then sprinkle on a bit of Parmesan cheese, if you like. Bake the frittatas until they are puffy and the edges are golden brown, about 20-25 minutes. (If necessary, run a butter knife around the edge of each one to loosen them before removing them from the pan. Makes 6 mini- frittatas. Add other ingredients as you like for taste.