01 - Preheat oven to 375°F. Lightly grease a standard 6-cup muffin tin or line with silicone muffin liners.
02 - In a skillet over medium heat, melt butter. Add minced garlic and sauté for 30 seconds until aromatic.
03 - Add chopped spinach and cook, stirring often, until wilted, about 2 minutes. Remove from heat to cool slightly.
04 - Whisk eggs, milk, salt, pepper, and nutmeg in a mixing bowl until smooth. Fold in mozzarella and Parmesan cheeses.
05 - Distribute sautéed spinach evenly among the muffin tin wells. Pour egg mixture over spinach, filling each well about three-quarters full.
06 - Place tin in the oven. Bake for 16 to 18 minutes, until the egg cups are set and lightly golden.
07 - Allow to cool for 2 to 3 minutes. Run a knife around the edges to loosen. Serve while warm.