Preheat oven to 200 degrees C. Grease a shallow baking pan.
Sift together the bakers flour, wholemeal flour, salt, bicarb soda and sugar in a bowl. Rub the butter into the flour mixture until combined. Make a well in the centre and pour in the combined oil and buttermilk. Stir to make a soft dough.
Lightly knead the dough on a floured surface for 1 minute. Place the dough into the prepared pan and pat into a round loaf. Cut a cross into the top of the loaf, brush with the extra buttermilk and sprinkle with the extra sugar.
Bake for 30 minutes. Reduce heat to 180 degrees C; rotate pan and bake another 30 minutes.