Preheat the oven to 325°F. Grease or line a baking sheet.
In a large bowl, whisk together the melted butter, sour cream, milk and sugar if using.
In another bowl, whisk flour with baking powder, soda, and salt.
Stir in mashed potatoes into wet mixture until well combined. Then stir in flour mixture until you have a shaggy dough.
Stir/fold in grated cheese, if using, until combined. Fold in the chopped chives.
With hands knead for a minute until you have a dough that is not sticky. Add a little more flour if necessary. Transfer to a floured clean surface and pat or roll dough until it is about an inch high. Cut dough into 8 wedges or punch out dough with round cookie cutters. You can re-roll scraps (they won’t look so nice baked up BIUT will taste just as good).
Place on greased or lined baking sheet and bake for 15-20 minutes (depending on size of biscuits) or until puffed and golden brown.