Preheat your oven to 400°F (200°C) and grease a muffin tin.
In a mixing bowl, beat the eggs and mix in the sour cream until well combined.
Add the shredded cheddar cheese, Parmesan cheese, chopped chives, and a pinch of salt to the egg mixture. Mix thoroughly.
Gently fold in the mashed potatoes, ensuring the mixture is evenly combined.
Spoon the mixture into the greased muffin tin, filling each cup to the top.
Bake in the preheated oven for about 20-25 minutes, or until the tops are golden brown and puffed up.
Allow the potato puffs to cool slightly before carefully removing them from the muffin tin.
Serve the leftover mashed potato puffs as a delicious side dish or snack.