Nonstick spray or butter for greasing baking sheet
3 cups all purpose flour
3 cups whole wheat flour
1/2 cup packed brown sugar
1 tsp baking soda
1/2 stick chilled butter, cut into 1/2 inch cubes
2 cups buttermilk
Preheat oven to 425F. Prep a baking sheet with nonstick spray.
Whisk together both flours, sugar, and the baking soda in a medium bowl. Add the butter and cut in until the putter pieces are not bigger than a pea. Add in the buttermilk and stir until dough is moistened. Turn dough out onto a floured work surface and knead until dough comes together, about 10 turns. Shape dough into a 7 inch round and place on the prepared baking sheet. Cut a x, 1/2 inches deep in the top of the dough.
Bake until deep brown and bottom sounds hollow, about 40 minutes. Transfer to a rack to cool.