Slice the butter into cubes and measure out the buttermilk. Place both in the freezer for about 10 minutes.
Begin preheating the oven to 400° F (204° C) and set out a baking sheet.
Place all of the dry ingredients, the flours, baking powder, baking soda, and salt in a large bowl and fluff to combine and aerate.
Add the butter to the bowl and with a pastry cutter or two forks, work the butter into the flour until the butter is about pea-sized. There will be smaller and larger crumbs; this is correct.
Pour the buttermilk into the bowl and stir together with a fork until large lumps of dough form. Not everything will be mixed together.
Lightly flour a work surface and dump out the bowl contents onto it. Without kneading or pushing the dough together too much, gently form a rectangle. Not all of the dough will come together at this point.
Fold one third of the dough over the middle. Fold the other third over the top. The dough will still be very loose.
Spin the dough 90 degrees and flatten the dough into a rectangle again. Repeat the folding and rectangle forming for about 4-6 times. It will become cohesive by this point.
Flatten the dough to about 3/4” thick and with a 2 1/2” round cookie cutter dipped in flour, cut out the biscuit circles. Push the cut ends back into the whole dough to avoid reshaping and overworking.
Place the biscuit rounds on the baking sheet and bake for about 18-20 minutes.