The key to flaky biscuits is little pockets of butter that create layers. Cold butter will not melt, creating these pockets and allowing the dough to not be overworked.
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1. Preheat oven to 450F. Sift together dry ingredients in a large bowl. Add frozen butter and shortening and work into the flour quickly by hand until resembling coarse crumbs.
2. Make a well in the center of flour mixture and add buttermilk. Stir with a wooden spoon gently, careful not to overwork. Mixture will be very sticky. Fold the dough over itself with the spoon one or two times to pick up any remaining flour in the bowl. Dust the top with flour and turn dough out onto a floured table.
3. With floured hands, fold dough over itself about 6-8 times. Then make a 1-inch thick pillow. Cut biscuits out with 2-inch biscuit cutter or glass turned upside down, pressing straight down, careful not to twist. Arrange on a greased baking sheet making sure the biscuits barely touch each other.
4. Bake 15-20 minutes, brushing with melted butter in the last five minutes, if desired. Transfer immediately to tea towel lined basket and serve.