Step 1Heat the oven to 400 degrees. In a medium bowl, combine the yeast and lukewarm water, then set aside until the mixture is foamy, 5 to 10 minutes.
Step 2Meanwhile, in a large bowl, sift together the flour, sugar, baking powder, baking soda and salt. Cut in the shortening until the mixture resembles coarse meal. Add the buttermilk and stir until completely blended. Stir wet ingredients into the dry ingredients with a fork.
Step 3Flour your hands and gather the dough into a ball. On a floured surface, knead the dough until soft and smooth, adding more flour as necessary to reduce stickiness, about 5 minutes.
Step 4Roll out the dough to a thickness of about half an inch. Using a 2-inch-round cutter, stamp out the biscuits and place them close together on a baking sheet. Gather the scraps, pat out the dough, and continue cutting rounds until the dough is used. Cover with a kitchen towel and set aside to rise in a warm place until almost doubled, about an hour.
Step 5Bake the biscuits for 10 to 15 minutes, or until nicely browned.