Graham flour is coarser than regular whole-wheat flour, which also works. If you use the latter, 
substitute one-half cup wheat bran for one-half cup all-purpose flour.
 
Ingredients  
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

Directions 
1. Preheat oven to 350*F. Line a baking sheet with parchment paper; set aside. Whisk 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 resembles small peas. Add buttermilk all at once; stir with a fork until mixture holds together.
 
2. In the bowl, pat the dough into a domeshaped loaf about 7 inches in diameter. Lift out dough; transfer to lined sheet.
 
3. 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.  Serves 4 to 6.

Source:  www.marthastewart.com