1. Preheat oven to 500°. Whisk together first 2 ingredients in a large bowl. Cut in cold butter and shortening with a pastry blender until mixture resembles small peas and dough is crumbly. Cover and chill 10 minutes. Add buttermilk, stirring just until dry ingredients are moistened.
2. Turn dough out onto a heavily floured surface; knead 3 or 4 times. Pat dough into a 3/4-inch-thick circle.
3. Cut dough with a well-floured 2 1/2-inch round cutter, rerolling scraps as needed. Sprinkle cornmeal on ungreased baking sheets; place biscuits on baking sheets. Lightly brush tops with 2 Tbsp. melted butter.
4. Bake at 500° for 13 to 15 minutes or until golden brown.
Note: We tested with White Lily Bleached Self-Rising Flour.