Preheat your oven to 400°F. Grease a muffin tin with butter or spray.
In a large bowl, combine mashed potatoes, eggs, cheddar, Parmesan, chives, salt, and pepper. Mix until smooth.
Scoop the mixture into the muffin tin cups, filling each about 3/4 full.
Bake for 30–35 minutes until the tops are golden and lightly crispy.
Let cool a few minutes before popping them out with a spoon. Serve warm.