Preheat the oven to 400F. Place both flours and baking soda into a mixing bowl and stir it up. Make a crater in the middle and pour in half the buttermilk.
Using your hands (flour them first), turn the mixture over and gather it into a dough. Add the rest of the buttermilk and begin to knead the dough into a round, cake-like shape. Don't over-knead and don't take too long over it.
Place on a wooden cutting board and cut a large 'x' into the top surface.
Place into pre-heated oven on a baking sheet for about 30-35 minutes. When done, the bread should appear browned on top and the loaf should sound 'hollow' when you tap the bottom of it with your knuckle. Allow to cool on a wire rack.
To keep in moisture, keep covered with a cotton dish towel. Consider placing the loaf in a sealed plastic bag overnight to keep it fresh.
Delicious with jam in the mornings, with soup at lunch or with smoked salmon; the latter is commonly served as hors doevres at Irish parties. A little hunk of Ireland on your table!