Adapted from Cook's Illustrated
2 1/2 cups flour plus more for rolling dough
1 tablespoon baking powder
1/2 teaspoon baking soda
1/2 teaspoon salt
1 tablespoon sugar
2 tablespoons shortening
1 stick very cold butter
1 1/4 cup very cold buttermilk
Preheat oven to 450º. Line baking sheet with silpat or parchment paper.
In a bowl, whisk together dry ingredients. Cut in shortening in with pastry blender or a couple knives till the size of peas. Cut butter into 8 pieces and, one at a time, rub them into the flour with your fingers till they are flattened into thin sheets (they will break apart). You'll want all the butter separated into these pieces so when they melt in the oven, they will make the biscuits flaky.
Put the bowl in the freezer for 15 minutes.
Add all the buttermilk except the last two tablespoons. Mix gently with a spatula. If the dough is too dry, you may add the remaining buttermilk. Lightly flour another silpat and roll the dough out to cover the surface (11 x 16). Fold the dough into thirds, then roll to an inch thick.
Cut into biscuits using sharp round cutter...3 inch diameter or less...press straight down without twisting. Dip the cutter into flour if it sticks to the dough. Pat together scraps to make last few biscuits. Place biscuits on lined baking sheet, and bake about 15 minutes or till lightly browned. Makes 6-9 depending on size of your cutter.