1.Preheat oven to 425 degrees F (220 degrees C).
2.Line a baking sheet with a silicone baking mat or parchment paper.
3.Whisk flour, baking powder, salt, and baking soda together in a large bowl.
4.Cut butter into flour mixture with a pastry blender until the mixture resembles coarse crumbs, about 5 minutes.
5.Make a well in the center of butter and flour mixture. Pour in 3/4 cup buttermilk; stir until just combined.
6.Turn dough onto a floured work surface, pat together into a rectangle.
7.Fold the rectangle in thirds. Turn dough a half turn, gather any crumbs, and flatten back into a rectangle. Repeat twice more, folding and pressing dough a total of three times.
8.Roll dough on a floured surface to about 1/2 inch thick.
9.Cut out 12 biscuits using a 2 1/2-inch round biscuit cutter.
10.Transfer biscuits to the prepared baking sheet. Press an indent into the top of each biscuit with your thumb.
11.Brush the tops of biscuits with 2 tablespoons buttermilk.
12.Bake in the preheated oven until browned, about 15 minutes.