How to Make It
Preheat oven to 425°F. Line a baking sheet with parchment paper. Whisk together flour, baking powder, baking soda, black pepper, and salt in a large bowl until combined. Using a pastry blender or your fingers, work cold butter into flour mixture until butter is in small, flattened pieces and mixture is crumbly. Stir in scallions and 1/2 cup cheese. Add 3/4 cup buttermilk, and stir just until dough comes together, adding up to 1/4 cup additional buttermilk, 1 tablespoon at a time, if necessary. (Dough should be neither sticky nor crumbly.)
Transfer dough to a lightly floured surface, and knead 3 to 4 times just to bring dough together. Pat dough into an 8- x 6-inch rectangle; fold 1 short side a third of the way over toward center. Fold opposite short side over folded end (business letter fold). Rotate dough clockwise 90 degrees; pat out dough into a 8- x 6-inch rectangle, and repeat folding procedure. Pat dough out into an 8- x 6-inch rectangle (3/4 to 1 inch thick); cut dough into 8 rectangular biscuits.
Sprinkle remaining 1/2 cup cheese into 8 mounds about 3 inches apart on prepared baking sheet, scattering cheese just a bit so some cheese will stick out from under biscuits. Place each biscuit rectangle on a mound of cheese on baking sheet. Brush tops with melted butter. Bake biscuits in preheated oven until golden brown, about 15 minutes.