Preheat oven to 425ºF. Line a baking sheet with parchment paper and set aside.

In a large bowl, add flour, brown sugar, cocoa powder, baking powder, baking soda, and salt. Whisk to combine.

Add cold butter cubes to bowl. Cut the butter into the flour mixture using a pastry blender until a crumbly dough forms.

Combine buttermilk and vanilla and add to the dough. Toss gently using a fork just until all of the dough is moistened and there's no dry flour. Do not stir or over mix the dough. 

Transfer the dough onto a lightly floured surface. If necessary, use your hands to gently bring the dough together. Roll out the dough into a circle that's 1 inch thick. Use a 2.5 inch round cutter to cut 6 biscuits from the dough (you will need to re-roll dough scraps to get 6 biscuits).

Place the dough circles 1 inch apart on the prepared baking sheet. Bake for 13-15 minutes, or until a toothpick inserted into the side of a biscuit comes out clean. Let biscuits cool on a wire rack or serve warm.