Preheat the oven to 425°F. Line a baking sheet with parchment paper or spritz with cooking spray.
In a large bowl use a whisk to sift together the flour, sugar, baking powder, baking soda, garlic salt and onion powder.
Cut the butter into the dry ingredients with a pastry blender until it resembles coarse crumbs.
In a separate medium bowl whisk the egg with the buttermilk. Make a well in the center of the dry ingredients and add the wet to the dry.
Use a fork to work the liquid into the flour using a circular motion. Keep mixing until the flour is nearly moistened. Add the mashed potatoes mixing into the dough using the same technique.
After everything has combined, the dough will look a little lumpy. Add the shredded cheese and chopped chives. Mix until fully combined.
Turn dough out onto a lightly floured surface and knead gently several times until the dough holds together.
Roll to 1/2-inch thickness and use a 3-inch biscuit cutter or glass dipped in flour to cut into circles.Re-roll the scraps and repeat until all of the dough has been used.
Place the dough rounds onto the baking sheet and brush the tops with melted butter.
Bake for 18-20 minutes or until the tops and bottoms are lightly golden. Serve warm.