1. Preheat oven to 400°. Combine yeast and warm water in a 1-cup glass measuring cup; let stand 5 minutes.
2. Meanwhile, whisk together flour and next 4 ingredients in a large bowl; cut in shortening and butter with a pastry blender until crumbly.
3. Combine yeast mixture and buttermilk, and add to flour mixture, stirring just until dry ingredients are moistened. Turn dough out onto a lightly floured surface, and knead about 1 minute.
4. Roll dough to 1/2-inch thickness. Cut with a 2-inch round cutter or into 2-inch squares. Place on 2 ungreased baking sheets.
5. Bake at 400° for 12 to 15 minutes or until golden.
Cinnamon-Raisin Angel Biscuits: Substitute 1/4 cup firmly packed brown sugar for 2 Tbsp. sugar. Stir 1 cup baking raisins, 2 tsp. lemon zest, and 1 tsp. ground cinnamon into flour mixture in Step 2. Proceed with recipe as directed.
Note: We tested with Sun-Maid Baking Raisins.
Time-Saving Tips: Prepare recipe as directed through Step 3. Shape dough into a disk; store in a glass, airtight container in refrigerator up to 5 days. Let stand at room temperature 5 minutes. Roll, cut, and bake as directed in Steps 4-5. Unbaked biscuits may be frozen on a baking sheet, covered with plastic wrap, 2 hours. Transfer frozen biscuits to a zip-top plastic freezer bag, and freeze up to 1 month. Let stand at room temperature 30 minutes before baking as directed.