Preheat your oven to 400°F (200°C) and lightly grease a 12-cup muffin tin.
In a mixing bowl, combine the cold mashed potatoes, eggs, cheddar cheese, Parmesan, and chopped chives. Season with salt and pepper.
Mix until all ingredients are fully incorporated.
Scoop the mixture evenly into the muffin tin cups, filling each about 3/4 full.
Bake for 20–25 minutes or until the tops are golden brown and crispy.
Allow to cool for a few minutes, then gently remove from the tin and serve warm.