1. 1. Preheat your oven to 400 F (200 C). Lightly grease a 9-inch cast-iron skillet or an 8×8 inch baking dish.

2. 2. In a large mixing bowl, whisk together the all-purpose flour, baking powder, baking soda, and salt.

3. 3. Add the cold, cubed butter to the dry ingredients. Using a pastry blender, two knives, or your fingertips, cut the butter into the flour mixture until it resembles coarse crumbs with some pea-sized pieces of butter remaining.

4. 4. Fold in the shredded cheddar cheese. Then, add the sourdough discard and ¼ cup of milk. Mix with a spoon or your hands until just combined. Do not overmix.

5. 5. Turn the dough out onto a lightly floured surface. Gently pat the dough into a round or square shape about ¾ to 1 inch thick. Cut the dough into 8-10 squares or wedges using a knife or bench scraper, or use a biscuit cutter for rounds.

6. 6. Place the biscuits snugly in the prepared skillet or baking dish. If desired, brush the tops with a little extra milk for a golden finish.

7. 7. Bake for 15-20 minutes, or until the tops are golden brown and the biscuits are cooked through.

8. 8. Remove the skillet from the oven and let the biscuits cool for a few minutes before serving. They are best enjoyed warm, straight from the skillet.