Sieve cream flour, salt, and bread soda into a bowl. Mix in the bran and wholemeal flour. Add the oil and sufficient buttermilk to make a soft dough. Turn onto a lightly floured board and knead.
Shape into a round and place in a deep 7-inch cake tin. Cut a cross on the top of the dough. Cook in a pre-heated oven at 2200C / 4250F / Gas 7 for approximately 40 minutes.