In large mixing bowl, combine flour, sugar, baking soda and salt. Using a pastry blender or two forks, cut shortening and 4 tablespoons butter into flour until it resembles coarse crumbs.
Make a well in the flour; pour in buttermilk. Gently fold flour into buttermilk until a sticky dough is formed. Turn dough out onto a floured work surface; dust with flour. Gently fold dough over itself 5-6 times to create layers.
Roll dough out to ¾-inch thick. Cut with a 2½-inch biscuit cutter or upside-down drinking glass. Place biscuits onto an ungreased baking sheet. Melt remaining 2 tablespoons butter; brush over biscuits.
Bake in a preheated 425°F oven 15 minutes or until golden brown.