Preheat oven to 350° F. Spray 2 mini muffin tins (with 24 cups each) with nonstick spray. Set aside.

In a medium bowl, whisk the eggs, milk, and 3/4 cup of the Parmesan. Season with salt and pepper, keeping in mind that the Parmesan will add plenty of salty flavor. Set aside.

In a large skillet over medium-high heat, heat the butter and olive oil. Add the pepper, onion, and garlic and sauté just until softened, about 5 minutes or so. Add the ham to the pan and stir together. Take pan off heat. Divide the mixture between 40 (give or take, depending on your ingredients and size of muffin cups) muffin cups and then fill the remaining area of the muffin cup almost to the top with the egg mixture. Give a little stir to combine the egg mixture with the veggies and ham. Top each muffin cup with a slice of tomato and a bit of chives, and then sprinkle with a little more of the remaining 1/4 cup of Parmesan. If desired, add a little freshly cracked black pepper over the top.

Bake for 12 to 14 minutes, or until eggs puff up and are just set in the center.

Remove from oven and let rest in pan for at least 5 minutes before removing (they'll come out much easier!). Serve warm or at room temperature.

The mini frittatas keep well in a covered container in the refrigerator for a few days, and make for a quick and delicious grab-and-go breakfast.