Yeast is used as part of the leavening to give these easy angel biscuits the light, airy texture that inspired their name.
In a medium bowl, sift or whisk together flour, sugar, baking soda, baking powder, and salt; set aside. Sprinkle yeast over water, and allow to stand until creamy looking, about 5 minutes.
In a medium bowl, combine 1 cup of the flour mixture, yeast mixture, melted butter, and 1 cup buttermilk. Stir to combine. Add the remaining flour and buttermilk alternately, stirring between additions. When a sticky dough forms, cover it with plastic wrap, and place in the refrigerator for 2 hours.
Preheat oven to 450 degrees. Remove dough from refrigerator, and turn out onto a lightly floured work surface. Knead a few times, and roll to a 1/2-inch thickness. Cut out with a 2 1/4-inch round biscuit or cookie cutter, and place on baking sheet about 1 inch apart. Bake 12 to 15 minutes or until golden on top and done in middle. Remove from oven; cool on a wire rack. Serve warm.