1 1/2 cups all-purpose white flour
1 1/2 cups whole-wheat flour
1/2 cup cake flour (use all-purpose if you don't have cake flour)
1/2 cup wheat germ or oat bran
2 tablespoons sugar
1 1/2 teaspoons baking soda
1 1/2 teaspoons cream of tartar
1 1/2 teaspoons salt
2 tablespoons butter, softened
1 1/2 cups buttermilk
Place flours, wheat germ, sugar, baking soda, cream of tartar, and salt in a large bowl and whisk until fully combined. With your fingers, rub softened butter into the flour mixture until completely incorporated. Create a well by pushing some of the flour to the sides of the bowl, and pour in the buttermilk. With a fork, stir the mixture gently to incorporate the buttermilk into the dry ingredients. The dough will come together in large clumps.
Turn dough out onto a lightly floured surface and use your hands to bring it together to form a 6-inch round. It will be a little uneven; don't worry! Place the dough in a 12-inch cast iron, or on a baking sheet, and score a deep cross into the top of the bread, nearly reaching each edge, and about half an inch deep. Bake bread at 400 degrees for 40–45 minutes, or until a toothpick comes out clean. Let cool for about 20 minutes. Best served warm with butter.