Heat oven to 350°F. Coat 12-cup muffin pan with nonstick cooking spray.
In large bowl, whisk together eggs, milk, ½ teaspoon each salt and pepper and ricotta, if using. Divide half of egg mixture among prepared muffin cups, followed by desired fillings (except grated cheese) and then remaining egg mixture. Top with grated cheese, if using. Bake until puffed and set, 20 to 25 minutes.
