Step 1 Place the flour, baking powder, salt, baking soda and butter in the bowl of a mixer and mix on low speed until it reaches a sand-like texture.
Step 2 Add the buttermilk slowly while mixing. Do not overwork. Form into 2 disks and refrigerate for 1 hour.
Step 3Flour a flat surface and roll out each disk 1/2 inch thick. Trim the dough about 1/2 inch larger than each of 2 (2-quart) casserole dishes that are 2 inches deep. Place each piece of dough on a baking sheet or floured board and poke holes across the top using a fork. Cover with plastic wrap and refrigerate.