Preheat oven to 375°F (190°C) and grease a muffin tin with cooking spray or butter.
In a large bowl, combine mashed potatoes, shredded cheddar cheese, Parmesan cheese, eggs, flour, and seasonings.
Mix well until fully incorporated.
Spoon the mixture into the muffin tin, filling each cup about 3/4 full.
Bake for 20-25 minutes or until golden brown and crispy on top.
Let cool for a few minutes before removing from the tin.
Garnish with chopped chives if desired and serve warm.