1. In a small bowl, sprinkle the yeast over 1/2 cup warm water; let stand until foamy, about 5 minutes. Into a large bowl, sift together flour, sugar, salt, baking powder, and baking soda; set aside.

2. Place 1 cup flour mixture in another large bowl. Add butter, yeast mixture, and 1 cup buttermilk; stir to combine. Add remaining flour mixture in three batches, alternating with remaining cup buttermilk and stirring between additions, until dough is sticky and just holds together. Cover bowl with plastic wrap; refrigerate at least 2 hours or overnight.

3. Preheat oven to 450 degrees. Pinch off 24 pieces of dough, and roll into 2-inch balls; place them, just touching one another, on a baking sheet. Bake until the biscuits are golden brown, 20 to 25 minutes. Serve warm. Once formed, the dough balls can be refrigerated overnight, covered with plastic wrap.