Preheat an oven to 375°F and position an oven rack in the center. Using cooking spray or canola oil, lightly coat muffin cups with oil.
Evenly divide the ham, corn and cheese between each muffin cup.
In a medium bowl, whisk to combine the eggs, milk, parsley, salt and pepper. Ladle the mixture over the ham and cheese, filling the cups three-quarters full.
Transfer the muffin tin to the oven and bake until the frittatas are puffed and set in the center, about 18 minutes.
To serve: Carefully run a knife around the edges to loosen and remove from the pan. Serve hot from the oven or cool completely on a wire rack, wrap individually and freeze for up to 1 month.