1. 1. Preheat your oven to 425 F (220 C). Lightly grease a 9-inch cast iron skillet or a small baking sheet. A cast iron skillet helps create a wonderfully crispy bottom crust.

2. 2. In a medium bowl, whisk together the all-purpose flour, baking powder, baking soda, and salt. Make sure there are no lumps and the ingredients are evenly distributed.

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. This step is crucial for flaky biscuits.

4. 4. Pour in the sourdough discard and milk. Stir with a spoon or spatula just until the mixture comes together and no dry streaks of flour remain. Be careful not to overmix, as this can lead to tough biscuits. The dough will be shaggy and sticky.

5. 5. Using a large spoon or an ice cream scoop, drop spoonfuls of the dough directly into the prepared skillet. You should get about 6-8 biscuits, depending on their size. Don’t worry if they aren’t perfectly shaped; they are “drop” biscuits, after all!

6. 6. Place the skillet in the preheated oven and bake for 15-20 minutes, or until the tops are golden brown and the biscuits are cooked through. A toothpick inserted into the center should come out clean.

7. 7. If desired, once the biscuits are out of the oven, brush the tops with a tablespoon of melted butter for extra shine and flavor.

8. 8. Let the biscuits cool in the skillet for a few minutes before serving them warm. They are best enjoyed fresh from the oven.