Preheat oven to 450°.
Place potato in a medium saucepan; cover with water. Bring to a boil. Reduce heat, and simmer 15 minutes or until tender; drain. Return potato to pan. Add buttermilk, sour cream, and butter to pan; mash with a potato masher until smooth.
Lightly spoon flour into dry measuring cups; level with a knife. Combine flour, baking powder, salt, and baking soda in a large bowl. Add potato mixture; stir just until moist. Turn dough out onto a lightly floured surface; knead lightly 5 times. Pat dough to 3/4-inch thickness. Cut with a 2-inch biscuit cutter into 15 biscuits. Place biscuits 2 inches apart on a baking sheet coated with cooking spray. Bake at 450° for 15 minutes or until lightly browned. Serve warm.