3 cups all-purpose flour, plus more for dusting
1 cup whole-wheat graham flour.
2 1/2 teaspoons coarse salt
1 teaspoon baking soda
1 teaspoon baking powder
4 tablespoons cold unsalted butter, cut into small pieces
1 2/3 cups buttermilk
Preheat oven to 350 degrees. Line a baking sheet with parchment paper; set aside. Whish together the flours, salt, baking soda, and baking powder in a large bowl. With a pastry blender or your fingertips, blend in butter until it ressembles small peas. Add buttermilk all at once; stir with a fork until mixture holds together.
In the bowl, pat the dough into a dome-shaped loaf about 7 inches in diameter. Lift out dough; transfer to lined sheet.
Lightly dust top of loaf with flour. Cut a 3/4 inch-deep cross in top, reaching almost all the way to edges. Bake, rotating sheet halfway through, until deep golden brown and a cake tester inserted into the center comes out clean, about 1 hour and 20 minutes. Let cool on a wire rack.