01 - Preheat oven to 375°F (190°C). Lightly grease a 6-cup muffin tin to prevent sticking.
02 - Combine softened butter, minced garlic, and chopped parsley in a small bowl until well mixed.
03 - Flatten each bread slice with a rolling pin. Trim crusts as needed so the slices fit into the muffin tin cups.
04 - Spread a thin layer of garlic butter on one side of each bread slice. Press each bread slice, butter side up, firmly into a muffin cup to form a nest.
05 - Sprinkle a small amount of grated Parmesan cheese into the base of each bread cup.
06 - Crack one egg into each bread cup. Season eggs with salt and black pepper. Top with shredded mozzarella or cheddar cheese if desired.
07 - Place muffin tin in the oven and bake for 16 to 18 minutes, or until egg whites are set and yolks are cooked to your preference.
08 - Allow egg cups to cool for 2 minutes. Carefully use a small spatula to loosen and remove each cup from the muffin tin.
09 - Serve warm. Garnish with additional chopped parsley, if desired.