MAKE AHEAD TIP:
You can easily freeze these little broccoli frittata muffins. Let them cool completely first and refrigerate for up to 3 days or freeze in a ziplock bag for up to a month. To reheat, either bake on low heat until warmed through or microwave for half a minute.
Brush the muffin tin with olive oil (You can also use a silicone muffin tray.) Combine the chopped broccoli, scallions, garlic, mint, or basil, and cheeses in a large bowl. Drizzle with olive oil and season to taste with salt and pepper. Spoon equal amounts of the broccoli mixture into the muffin cups.
Whisk the eggs, milk, salt and pepper together in a large bowl until the eggs are thick and frothy. Transfer the egg mixture to a pitcher and pour equal amounts into each muffin cup, over and around the broccoli mixture.
Bake for about 25 minutes, until set and golden. Remove, cool slightly, and invert the muffin tin to pop out the mini broccoli omelets. Serve warm or at room temperature.