How to Make It
Preheat the oven to 475°. Position a rack in the upper third of the oven. In a large bowl, whisk the 2 cups of flour with the salt, baking powder and baking soda. Using a pastry blender, cut in the shortening until the mixture resembles coarse meal. Using your fingers, rub in the sliced butter, leaving large flakes of coated butter. Freeze the mixture until very cold, about 15 minutes.
Stir in the buttermilk until a raggy dough forms. Transfer the dough to a lightly floured work surface and press or roll into a 9-by-7-inch rectangle, about 3/4 inch thick. Fold the rectangle in thirds like a letter, then fold the rectangle in half to make a little package. Press or roll out the dough to a 9-by-7-inch rectangle again. Repeat the folding process once more, then roll the dough out one more time to a 9-by-7-inch rectangle. Using a 3 1/2-inch round cutter, stamp out 4 biscuits. Pat the scraps together and stamp out 2 more biscuits.
Arrange the biscuits on a large baking sheet and brush the tops with the melted butter. Bake for about 14 minutes, shifting the baking sheet halfway through, until the tops and bottoms are golden and the biscuits are cooked through.