In a mixing bowl combine flour, baking powder and salt.
In a small bowl whisk together sourdough discard and milk. Then add to flour mixture.
Using a cheese grater, grate the very cold butter into mixing bowl. Then stir to combine. Once it starts to hold it's shape transfer to a floured work surface (countertop or cutting board).
Continue to work with hands until all dough in uniform. Roll out dough into a rectangle roughly 2 inches thick. Fold in the sides of the dough and roll out again. Do two more times, but on the final time roll out to 1½ inches thick.
Use a wide mouth canning jar lid (or the rim of a pint glass) to cut out 12 biscuits and place on a parchment paper covered baking sheet. Place in oven and bake for 15 minutes (or until golden brown on top).
Remove from oven and immediately brush each biscuit with melted butter.