Heat the oven to 425°F (220°C) and line a baking sheet with parchment paper or silicone mat.
In a large bowl, whisk together the flour, baking powder, baking soda, and salt.
1½ cups (200 grams) all-purpose flour, 2 teaspoons (7 grams) baking powder, ½ teaspoon baking soda, 1 teaspoon salt
Cut in the cold butter using a pastry cutter or your fingers until the mixture resembles coarse crumbs.
4 tablespoons (57 grams) unsalted butter
Stir in the cheddar cheese and green onions.
2 cups (227 grams) sharp cheddar cheese, ½ cup green onions
Add the sourdough discard and buttermilk, mixing with a spatula or your hands until just combined.
1 cup (250 grams) unfed sourdough discard, ¼ cup (60 milliliters) buttermilk
Turn the dough onto a lightly floured surface and gently pat it to about 1-inch thickness. Fold the dough into thirds like a business letter and then rotate the folded dough 90 degrees.
Repeat the folding and rotating three more times, then pat or roll out the dough to a rectangle 4 inches by 8 inches.
Use a bench scraper or biscuit cutter to cut out biscuits and place them on the prepared baking sheet. Brush with the melted butter, if using.
1 tablespoon melted butter
Bake for 12 to 14 minutes until the tops are a golden brown.