1. Preheat oven to 425°.
2. To prepare biscuits, weigh or lightly spoon flours and potato starch into dry measuring cups; level with a knife. Combine flours, potato starch, baking powder, and next 6 ingredients (through salt) in a medium bowl, stirring with a whisk; cut in shortening and butter with a pastry blender or 2 knives until mixture resembles coarse meal. Stir in cheese and parsley. Add buttermilk; stir just until moist.
3. Drop dough by 1/4 cupfuls 2 inches apart onto a baking sheet lined with parchment paper. Bake at 425° for 12 minutes or until golden brown.
4. While biscuits bake, combine melted butter and garlic powder in a small bowl; stir with a whisk.
5. Remove biscuits from baking sheet to a wire rack; brush with garlic butter. Cool slightly.