Preheat the oven to 450° F. In a medium-sized bowl, measure out the flours, baking soda, sugar, cinnamon, and salt. Whisk well.
Using the largest hole on a box cheese grater, grate the cold butter into the bowl. Stir the butter into the flour mixture, taking care to evenly distribute so as not to have any overly large clumps stuck together. Stir in the buttermilk until the mixture comes together and is moist.
Turn the dough out onto a floured surface and knead a few times until you can form a ball. Flatten the dough into a circle about 1/2 inch in thickness. Using a biscuit cutter, cookie cutter or a drinking glass (about 3" in diameter for the listed baking time) turned upside down, cut as many rounds as you can.
If desired, dip the tops in a cinnamon sugar mixture. Using the dough scraps, form another circle of the same thickness. Repeat cutting until you have used all the dough.
Place the biscuits on a parchment paper-lined baking sheet and bake at 450° F for 10-12 minutes. The biscuit tops should be lightly browned. Serve immediately.