1. Preheat the oven to Gas Mark 8/230C/450F.
2. Combine the flour, salt and bread soda. Make a well in the centre and add most of the buttermilk. Mix with your hand and add more milk if necessary. The dough should be soft but not sticky. Turn out onto a floured board and knead lightly. Shape into two rounds.
3. Flatten slightly to about 2 inches (5cm) deep. Put onto a baking sheet. Mark with a deep cross and bake in the oven for 15 minutes, then reduce the heat to 2000C/400F/Gas Mark 6 for about 20 minutes, or until the bread is cooked and sounds hollow when tapped.