Tall, flaky, and buttery biscuits with a subtle sourdough tang. Perfect for breakfast sandwiches, biscuits and gravy, or slathered with honey butter.

Preheat oven to 425°F (220°C). Line a baking sheet with parchment paper.
In a large bowl, whisk together the flour, baking powder, baking soda, sugar, and salt.
Grate the frozen butter on a box grater directly into the flour mixture. Toss gently to coat the butter shreds in flour.
Add the cold sourdough discard and buttermilk. Stir with a fork until the dough just comes together. It will be shaggy — that's perfect.
Turn the dough out onto a floured surface. Pat into a 1-inch thick rectangle. Fold in thirds like a letter. Rotate 90°, pat out again, and fold again. Repeat one more time (3 folds total). This creates the flaky layers.
Pat the dough to 1-inch thickness. Cut with a 2.5-inch biscuit cutter, pressing straight down (don't twist — twisting seals the layers).
Place biscuits on the prepared baking sheet with sides touching (this helps them rise taller).
Bake for 14-16 minutes until tall and golden brown on top.
Brush immediately with melted butter.