01 - Preheat oven to 375°F. Lightly grease a 6-cup muffin tin to prevent sticking.
02 - In a small bowl, blend softened butter with minced garlic and chopped parsley until evenly combined.
03 - Flatten each bread slice using a rolling pin. Trim crusts if necessary to fit the muffin tin.
04 - Spread a thin layer of garlic butter on one side of each flattened bread slice. Arrange each slice butter-side up into the muffin tin wells, pressing to form a nest shape.
05 - Sprinkle grated Parmesan cheese into the bottom of each bread cup.
06 - Crack one large egg into each bread-lined cup. Season with salt and pepper, and add shredded mozzarella or cheddar cheese if using.
07 - Bake in the preheated oven for 16 to 18 minutes, until egg whites have set and yolks reach desired level of doneness.
08 - Allow the cups to cool in the pan for 2 minutes. Carefully loosen and remove each using a small spatula.
09 - Serve warm, garnished with additional parsley if desired.