Mix the salt and bicarbonate of soda into the flour.
Put the flour in a bowl and make a well in the middle. Pour half of the buttermilk/milk into the well and use a knife to mix it with the flour. Add more milk until you have a soft, but not sticky, dough . Roll it in the last bits of flour or sprinkle with more flour to shape it into a ball.
Sprinkle some flour onto a baking tray. Place the ball of dough on the tray. Using a sharp knife, cut a deep cross across the top of the dough.
Place in an oven pre-heated to 425 F, 220 C, gas mark 7 for 30 minutes.
Check that it is cooked by turning it over and tapping the bottom. When it makes a good hollow sound it is cooked.
Cool on a wire rack until warm. Then slice and serve with butter.