Preheat the oven to 400°F and position the rack in the center. Grease each cup of a mini muffin tin lightly with cooking spray or butter.
In a large mixing bowl, combine the mashed potatoes, beaten eggs, 3/4 cup of the grated cheese, chives, and diced bacon or ham (if using). Stir until the mixture is well incorporated, seasoning with salt and pepper as needed.
Spoon the mashed potato mixture into the muffin cups, filling each one evenly. Top each filled cup with a sprinkle of the remaining 1/4 cup cheese.
Bake for approximately 20 minutes, or until the tops are golden brown and the puffs are fully set.
Allow the puffs to cool in the pan for about 5 minutes before carefully releasing them with a spoon or small knife. Serve immediately, adding a dollop of sour cream if desired.