Preheat oven to 450°.
Lightly spoon flour into dry measuring cups; level with a knife. Combine flour, sugar, baking powder, salt, and baking soda in a large bowl, stirring with a whisk. Cut in butter with a pastry blender or 2 knives until mixture resembles coarse meal. Add cheese and onions; toss well. Add buttermilk and sour cream; stir just until moist.
Drop dough by 1/4 cupfuls onto a baking sheet coated with cooking spray. Bake at 450° for 15 minutes or until edges are brown. Remove biscuits from pan; cool on wire racks.