Step 1: Prepare the Mashed Potatoes

1. Mash the potatoes (if not using leftovers): If you don’t have leftover mashed potatoes, start by boiling 2-3 medium-sized potatoes until tender. Drain, and mash with 1/4 cup milk, 2 tablespoons butter, and season with salt and pepper. The mashed potatoes should be smooth and creamy but not overly wet.
2. Cool the potatoes: Allow the mashed potatoes to cool slightly before incorporating them into the muffin batter.

Step 2: Preheat the Oven

1. Set the oven: Preheat your oven to 375°F (190°C). Grease a 12-cup muffin tin with non-stick spray or line with paper muffin cups.

Step 3: Mix the Dry Ingredients

1. Combine dry ingredients: In a large bowl, whisk together the flour, baking powder, baking soda, garlic powder (if using), and a pinch of salt and pepper.

Step 4: Mix the Wet Ingredients and Cheese

1. Combine the wet ingredients: In a separate bowl, beat the egg, sour cream (or Greek yogurt), melted butter, and milk until smooth. Stir in the cooled mashed potatoes until fully combined.
2. Add the cheese and chives: Fold in the shredded cheddar cheese and fresh chives into the potato mixture, reserving a small amount of each for topping.

Step 5: Make the Muffin Batter

1. Combine wet and dry ingredients: Gradually add the wet mixture to the dry ingredients, stirring gently until just combined. Be careful not to overmix, as this can make the muffins dense.

Step 6: Fill and Top the Muffin Cups

1. Fill the muffin tin: Divide the batter evenly between the prepared muffin cups, filling each about 3/4 full.
2. Top with cheese and chives: Sprinkle the tops of the muffins with a little extra shredded cheddar cheese and chopped chives for added flavor and presentation.

Step 7: Bake the Muffins

1. Bake: Place the muffin tin in the preheated oven and bake for 18-22 minutes, or until the muffins are golden brown on top and a toothpick inserted into the center comes out clean.
2. Cool: Remove the muffins from the oven and let them cool in the tin for a few minutes before transferring to a wire rack to cool completely.