How to Make It
Preheat the oven to 425°. In a large bowl, whisk together the flour, Parmigiano-Reggiano, chopped thyme, baking powder, salt, sugar and baking soda. Using a pastry cutter or 2 knives, cut in the chilled shortening and butter until the mixture resembles coarse meal. Add the buttermilk and mix gently until just incorporated.
On a floured work surface, using a rolling pin, gently roll out the dough to a 13-inch round, about 1/2 inch thick. With a 2 1/2-inch fluted biscuit cutter, cut out as many biscuits as possible. Transfer to 2 large baking sheets, leaving about 1 inch between biscuits. Gather the dough scraps, gently press them together and cut out 5 or 6 more biscuits.
Bake the biscuits for about 18 minutes, until they are golden brown and risen. Serve hot or warm.