How to Make It
Line a half-sheet pan with parchment paper.
In a large bowl, whisk together the flour, baking powder, sugar, salt, and baking soda. Add the shortening and use your fingertips to pinch it into the flour mixture to form small, pea sized pieces.
Drop the butter cubes into the flour mixture and toss until all of the pieces are coated. With your fingertips, press the cubes to flatten. Freeze the mixture in the bowl for 15 minutes.
Lightly coat your work surface with nonstick cooking spray, then flour. (The spray keeps the flour in place.) Reserve 1 tablespoon buttermilk in a small bowl and add the remaining to the flour mixture. Mix until the dough forms a shaggy ball and there are no dry bits of flour left. The dough should be slightly sticky.
Transfer dough to the prepared work surface. Lightly coat your hands with flour and gently press the dough with the heels of your hands to form it into a smooth flat disc, 1/2-inch thick. With a floured 1 1/2-inch biscuit cutter, cut out dough rounds. Flip the rounds over so that the smooth sides that were against the work surface face up and place on the prepared pan, 1-inch apart. Stack the scraps and press and cut again. Refrigerate until cold, about 15 minutes.
Preheat oven to 450°F. Stir the melted butter into the reserved buttermilk. Brush the tops of the biscuits with the butter mixture. Bake until the tops are golden brown and crisp, about 16 minutes. Let cool 5 minutes before serving hot.