1Preheat oven to 375F.
2In a large bowl, stir together the flours, baking powder, baking soda and salt. Add the butter and blend (or pulse the mixture in the food processor) until well combined and crumbly. If you like, add grated cheese, herbs, nuts or dried fruit at this point. Make a well in the middle of the flour mixture and add the buttermilk, stirring until blended.
3Knead a few times as you gather it into a ball. Place on a parchment-lined baking sheet and cut a deep X on top; brush with a little extra buttermilk.
4Bake for 1 hour, or until golden and the bread sounds hollow when tapped. Cool on a wire rack.