Preheat the oven to 350°F and lightly oil six muffin cups.
Whisk the eggs with the optional milk, salt, and black pepper until evenly combined.
Divide the feta, cherry tomatoes, basil, and spring onions among the prepared muffin cups.
Pour the egg mixture over the fillings, leaving a little room at the top of each cup.
Bake for 20 minutes, until the centers are set. Cool briefly before removing and serving.
Notes
Recipe facts extracted from the source page's embedded Healthy Breakfast Recipes (Egg Muffins) recipe card; the feta, cherry tomato, basil, and spring onion variation is used consistently.