Mix together the flours, salt, and baking soda in a large bowl. Add the butter and rub into the flour mixture with your fingertips until it resembles bread crumbs.
In a separate jug, whisk the egg and buttermilk together (see note on how to make Buttermilk below)
Make a well in the center of the dry ingredients and pour the liquid into the flour mixture.
Using an open hand bring the flour and liquid together to a loose dough. The dough should be quite soft, but not too sticky.
Turn onto a floured work surface and gently bring the dough together into a round about 1½ inches (4cm) thick (8 inches by 8 inches) .
Place on a baking sheet dusted well with flour
Score the bread by blessing it with a deep cross on top. Poke a hole in the 4 corners of the bread to release the fairies and stop them from cursing your beautiful bread.
Glaze the bread with the leftover bit of buttermilk in your jug and dust the top with rolled oats.
Bake for 15 minutes, then turn down the oven to 400°F (200°C) and bake for 30 minutes more. When done, the loaf will sound slightly hollow when tapped on the bottom. Remove from the baking sheet and place on a wire rack to cool.