First things first, preheat your oven to 375°F (190°C). This ensures the oven is at the right temperature to cook the puffs evenly and make them crispy. While it’s heating, prepare a baking sheet by lining it with parchment paper or giving it a light greasing. This small step is crucial to prevent the puffs from sticking.
In a large bowl, it's time to bring everything together. Combine the cold mashed potatoes, shredded cheddar cheese, egg, bread crumbs, chopped green onions, melted butter, garlic powder, salt, and pepper. Use a sturdy spoon or spatula to mix until all the ingredients are well incorporated and you have a consistent mixture.
Now for the fun part! Scoop about one to two tablespoons of the potato mixture. You can use a small cookie scoop for uniform size. Roll the mixture into a ball between your palms, then gently flatten it into a small, disc-like puff shape. Place each puff on your prepared baking sheet, leaving a little space between each one.
Once all your puffs are formed and arranged, you can give them an extra cheesy boost. If you're using it, sprinkle a little grated parmesan cheese over the top of each puff. Place the baking sheet in your preheated oven and bake for 20-25 minutes. You'll know they're ready when they are a beautiful golden-brown color and look crispy on the outside.
Carefully remove the baking sheet from the oven. I always let the puffs cool for a few minutes directly on the sheet before transferring them to a serving platter. This helps them firm up a bit so they don't fall apart. Serve them warm and enjoy the delicious, cheesy goodness!