These crunchy, golden biscuits are full of nutty, slightly sweet flavours. They are sliced from a long piece of dough, which you can make ahead and store in the refrigerator or freezer. So you can bake the biscuits all at once or in batches.
Sift the flour, baking powder and bicarbonate of soda into a mixing bowl, tipping in any bran left in the sieve. Add the oatmeal, bran and sugar, and mix well to combine.
Add the margarine and rub it in with your fingertips until the mixture resembles breadcrumbs. Add 3 tablespoons milk and stir in well so the mixture forms a soft dough. If the mixture is a little dry, add the remaining 1 tablespoon milk.
Turn the dough out onto a sheet of plastic wrap and shape it into a log about 25 cm long. Wrap the plastic around the dough and roll it gently back and forwards to make a smooth shape. Twist the ends of the plastic together to seal. Chill the dough for about 30 minutes. (It can be kept for up to 4 days in the refrigerator.)
Preheat the oven to 190ºC. Unwrap the dough and, using a very sharp knife, cut it across into slices 1 cm thick. Use greaseproof paper to line a baking tray and place the dough slices on it. Bake for about 12 minutes or until lightly browned.
Transfer the biscuits to a wire rack and leave to cool completely. They can be kept in an airtight container for up to 5 days.