Chadwick Boyd's biscuits get an upgrade from a thyme-infused mash of potatoes, celery root, and cream. Substitute 1 1/2 cups mashed potatoes, if desired. Run your hands under very cold water and dry well before working butter into flour in step 2 and working the dough in step 3. "This is the granny method," says Boyd. "It's the tactile way of merging the butter and flour—with your hands. You literally snap it between your fingers and thumb."