Measure 1 1/4 cups of Sourdough Discard and place it in the fridge for 15-20 mins before you start this recipe. Also, it helps if your flour is cold. Measure out 4 1/2 cups of flour and the 1/2 tsp of baking powder into a bowl and place it in the freezer for 15-20 minutes as well.
Line a large baking sheet with parchment paper. Preheat the oven to 450°.
*** Grab your Kitchenaid Mixing bowl and pour in the chilled 4 1/2 cups of Flour, 1/2 tsp of Baking Soda, 1 1/4 cup chilled Sourdough Discard, and 3/8 cup Buttermilk.
Next, grate the 12 tbsp of butter with your cheese grater and scoop all of that into the mixing bowl too. Use the dough hook attachment and mix just until the dough comes together. Do not overmix. You may need to add more buttermilk if the dough seems dry. Everyone's discard will be of different thickness (hydration) causing variation in the dough.
Dump the dough out onto a floured counter and flour your rolling pin, roll the dough out into a 12x6 rectangle. Fold each of the long edges into the middle, and then fold the bottom short edge up, and the top short edge all the way down over the bottom fold you just made. Then roll the dough out again until it is 1" thick. Use your 2 1/2" cutter to cut out the biscuits. Press firmly down, but do not twist the cutter as this will cause the layers you just made to seal and the biscuits won't rise as well. Gather up the scraps, re-roll, and cut more biscuits until the dough is gone.
Place the biscuits on the baking sheet leaving 1" of room between them. Brush the tops of the biscuits with buttermilk. Place them in the oven, on the middle rack, and bake them for 15-20 minutes or until golden brown. Remove them from the oven, brush them with the melted 2 tbsp of butter, and enjoy once they're cool enough to pick up!