How to Make It
Preheat oven to 425°.
Weigh or lightly spoon flour into dry measuring cups; level with a knife. Combine flour, oats, baking powder, sugar, and salt in a large bowl; cut in butter with a pastry blender or 2 knives until mixture resembles coarse meal. Fold in cranberries and rosemary. Chill for 15 minutes. Add buttermilk to flour mixture; stir just until moist.
Turn dough out onto a lightly floured surface; knead gently until dough just comes together. Divide dough in half; wrap 1 piece in plastic wrap, and refrigerate. Roll remaining dough into a 1/2-inch-thick (8 x 4-inch) rectangle; dust top of dough with flour. Fold dough crosswise into thirds (as if folding a piece of paper to fit into an envelope). Reroll dough into a 1/2-inch-thick (8 x 4-inch) rectangle; dust top of dough with flour. Cut dough with a 2-inch biscuit cutter to form 6 rounds, rerolling scraps as needed. Place dough rounds 1 inch apart on a baking sheet lined with parchment paper. Repeat procedure with remaining piece of dough. Bake at 425° for 12 minutes or until golden. Remove from pan; cool 2 minutes on wire racks. Serve warm.