Preheat oven to 350 degrees. Cook bacon or sausage, drain fat. Meanwhile, mix eggs, milk, and salt and pepper. Coat a muffin tin well with non stick cooking spray. Using a soup ladle, evenly distribute the eggs. Evenly distribute the breakfast meat. Finally, add cheese to each cup. Using a fork, gently stir, ensuring all ingredients are mixed into the egg. Wipe off any spilled egg from the top of the pan.
Cook frittatas for 15-18 minutes, or until there are no runny spots on top of the eggs. There will be a small amount of carryover cooking when you take them out of the oven.