Preheat your oven to 425 degrees
In a large bowl, combine 220 grams of all purpose flour, 240 grams of whole wheat flour, 1 1/2 teaspoons of baking soda and 1 teaspoon of salt
Add 450ml of buttermilk and mix until the ingredients are combined into a soft dough
Transfer the dough onto a floured surface and quickly knead just a few times to bring the dough together (no longer than 30 seconds)
Shape the dough into a round disk and transfer onto a parchment lined baking sheet
Use a very sharp knife or bread scoring knife to cut a large X over the top surface of the dough no deeper than 1/4”
Transfer into a 425 degree oven and bake for 20 minutes and then reduce the oven temperature to 375 degrees and bake for another 15-20 minutes or until the loaf is golden brown and sounds hollow when tapped on
Transfer the loaf to a cooling rack and let it color 30 minutes before slicing
Store in an airtight container at room temperature