Krumpli Pogácsa (Hungarian Potato Biscuits)

Ingredients

• 2 cups mashed potatoes, cooled
• 2½ cups all-purpose flour
• ½ cup unsalted butter, softened
• 1 egg
• 1 teaspoon salt
• 1 teaspoon baking powder
• 1 teaspoon sugar
• 2 tablespoons sour cream
• 1 tablespoon milk, if needed