01 - Preheat oven to 375°F (190°C). Lightly grease a 6-cup muffin tin.
02 - In a small bowl, thoroughly blend the softened butter, minced garlic, and chopped parsley.
03 - Use a rolling pin to flatten each bread slice. Trim the crusts if necessary to fit the muffin cups.
04 - Spread a thin layer of garlic butter on one side of each flattened bread slice. Press each bread slice, butter-side-up, into a muffin cup to create a nest shape.
05 - Distribute the grated Parmesan cheese evenly among the bread cups, sprinkling a portion into the bottom of each nest.
06 - Crack one large egg into each bread cup. Season lightly with salt and black pepper. Top with shredded mozzarella or cheddar cheese if desired.
07 - Place muffin tin in the preheated oven and bake for 16 to 18 minutes, until egg whites are set and yolks reach preferred doneness.
08 - Remove muffin tin from oven. Allow to cool for 2 minutes, then carefully release each cup using a small spatula.
09 - Transfer egg cups to plates. Serve warm, optionally garnished with additional chopped parsley.