- Preheat the oven to 450 degrees and line a rimmed baking sheet with parchment paper.
- In a large bowl, whisk together flour, baking powder, and sugar. Scatter chilled shortening and butter over flour mixture, and toss lightly to coat shortening and butter.
- With a pastry blender or two forks, cut in shortening and butter until the mixture is crumbly. The crumbles should be pea-sized and the flour should start to look like wet sand. Add buttermilk, stirring just until the dry ingredients are moistened.
- Turn the dough out onto a floured surface and sprinkle with self-rising flour. Kneed dough 4 to 5 times or until it is smooth and springy to the touch. Keep dusting with flour to keep dough from sticking to the work surface. Pat the dough down to a ¾-inch thickness.
- Cut out the biscuits with a floured 2-inch cutter, being careful not to twist the cutter. (Twisting the cutter can seal the edges of the biscuit, which could prevent the biscuits from rising.) Reshape the scraps as needed to finish cutting.
- Place biscuits with sides touching on prepared baking sheet. Bake for 13 to 15 minutes or until golden brown. Remove from oven and brush tops of baked biscuits with melted salted butter. Let cool completely on baking sheet. Serve warm or store in an airtight container.