Adapted from Gordon Ramsay's Home Cooking
2 cups all purpose flour plus extra for dusting
1 1/4 cups whole wheat flour
1 1/2 tsp baking soda
1 tsp salt
1 tsp sugar
2 cups buttermilk
Preheat oven to 400 degrees. Line baking sheet with parchment paper and dust with flour. Set aside.
Sift the flours, baking soda, salt, and sugar in large bowl. Make a well in centre and add all but two tablespoons of the buttermilk. Mix with fork taking care not to overwork the dough, but ensure all of the dry ingredients have been incorporated. If necessary, add the reserved buttermilk.
Dust work surface with flour and lightly knead the dough for 30 seconds. Don't overwork the dough. Form dough into round shaped loaf and place on prepared baking sheet. Press down on dough to flatten slightly. With a serrated knife, score an "X" deeply into the top of the loaf.