Preheat the oven to 375°F. Line a baking sheet with parchment paper.
In a large bowl, combine the all-purpose flour, whole wheat flour, baking soda, baking powder, salt and brown sugar. Add the buttermilk and mix just until a soft dough forms.
Turn the dough onto a floured surface and knead gently for about 1 minute to blend the ingredients more thoroughly.
Form the dough into a ball and flatten slightly to form a 6 to 7-inch round. Dust with a little bit of flour and slash an “X” in the top with the tip of a sharp knife. Allow the bread to rest for 15 minutes.
Once rested, bake for 35 to 40 minutes, or until golden brown and crusty. Cool for 10 minutes on wire rack before slicing.