Preheat Oven: Preheat the oven to 400°F (200°C). Grease a mini muffin pan thoroughly to prevent sticking.
Combine Ingredients: In a large mixing bowl, combine the cold mashed potatoes, shredded cheddar cheese, chopped chives, flour, garlic powder, salt, and pepper. Add the egg and mix until well-blended.
Form and Roll: Shape the potato mixture into small balls. Roll each ball in grated Parmesan cheese, coating well, and then press each ball into the prepared muffin cups.
Bake: Place the muffin pan in the preheated oven and bake for 15-20 minutes, or until the edges turn golden and crispy.
Serve: Allow the puffs to cool slightly before removing from the pan. Serve warm and enjoy the cheesy, golden goodness!