1. 1. Prepare Your Dry Ingredients: In a large mixing bowl, whisk together the all-purpose flour, baking powder, baking soda, and salt. Make sure these dry ingredients are well combined to ensure even leavening throughout your biscuits.

2. 2. Cut in the Cold Butter: Add the very cold, cubed butter to the dry ingredients. Using your fingertips, a pastry blender, or two knives, 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 flakiness.

3. 3. Combine Wet Ingredients: In a separate medium bowl, whisk together the sourdough discard and the cold milk until just combined.

4. 4. Mix Wet and Dry: Pour the wet ingredient mixture into the dry ingredients. Stir gently with a wooden spoon or spatula until the dough just comes together. Be careful not to overmix, as this can lead to tough biscuits. The dough will be shaggy and a little sticky.

5. 5. Shape the Biscuits: Turn the dough out onto a lightly floured surface. Gently pat the dough into a rectangle about 1/2 to 3/4 inch thick. Fold the dough in half, then pat it down again. Repeat this folding and patting process 2-3 times. This creates layers without overworking the dough. Finally, pat the dough to a final thickness of about 1/2 inch.

6. 6. Cut and Arrange: Use a 2-inch biscuit cutter (or a knife to cut squares) to cut out your biscuits. Press straight down without twisting the cutter to maintain the layers. Place the cut biscuits onto a baking sheet lined with parchment paper, arranging them so they are just touching if you prefer softer sides, or slightly separated for crispier edges.

7. 7. Bake to Golden Perfection: Preheat your oven to 425 F (220 C). If desired, brush the tops of the biscuits with a little extra milk for a golden finish. Bake for 15-20 minutes, or until the tops are golden brown and the biscuits are puffed up.

8. 8. Serve Warm: Remove the biscuits from the oven and let them cool for a few minutes on the baking sheet before transferring to a wire rack. Serve warm with your favorite toppings.