Preheat the oven to 350°F and brush a nonstick muffin pan with olive oil or nonstick cooking spray.

In a large bowl, whisk together the eggs, milk, garlic, mustard, most of the dill (reserve a little for garnish), salt, and several grinds of pepper. Pour just a bit of the egg mixture into the bottom of each muffin cup. Divide the kale, tomatoes, scallions, and feta into each cup then pour the remaining egg mixture on top.

Bake for 20 to 22 minutes, or until the eggs are set. Season with salt and pepper to taste and garnish with the remaining dill. Store any remaining frittatas in the fridge.