1. Preheat oven to 425°.
2. Lightly spoon flour into dry measuring cups; level with a knife. Combine flour, baking powder, and salt in a large bowl. Cut in butter with a pastry blender or 2 knives until mixture resembles coarse meal. Stir in cheese, onion, and sage. Add milk to flour mixture; stir just until moist.
3. Turn dough out onto a lightly floured surface; knead lightly 4 to 5 times. Pat or roll dough to a 1-inch thickness; cut with a 2 1/2-inch biscuit cutter. Place biscuits 2 inches apart on a baking sheet coated with cooking spray. Coat tops of biscuits with cooking spray.
4. Bake at 425° for 15 minutes or until lightly browned.