Preheat the oven to 425°F. Line a baking sheet with parchment paper or lightly grease a cast iron skillet.

In a large bowl, whisk together the flour, baking powder, sugar, salt, and baking soda.

Add the cold cubed butter and cut it into the flour mixture with a pastry cutter or your fingertips until crumbly with some pea-sized pieces remaining.

In a small bowl or measuring cup, stir together the sourdough discard and cold buttermilk.

Pour the wet mixture into the dry ingredients and stir gently just until a shaggy dough forms. Do not overmix.

Turn the dough onto a lightly floured surface and pat it into a rectangle about 1 inch thick.

Fold the dough in half, gently pat it out again, and repeat the folding process 2 to 3 times to create layers.

Pat the dough to about 1-inch thickness and cut out 8 biscuits with a round biscuit cutter, pressing straight down without twisting.

Place the biscuits on the prepared baking sheet or skillet with the sides just barely touching.

Bake for 13 to 15 minutes, until the tops are golden brown and the biscuits are puffed and set.

Brush with melted butter if desired. Cool for a few minutes and serve warm.