Rub the butter into the flour. Add the salt and soda, mix all well together by running the dry ingredients through your fingers.
Add the buttermilk (or sweet milk) and stir into a soft dough with a wooden spoon. With your floured hands, knead the dough lightly into a ball and turn out onto a lightly floured baking sheet.
Flatten the dough into a circle 1 1/2 inches thick with the palm of your hand. Make a cross in the center with a floured knife.
Bake at 425 degrees for 30 to 35 minutes.
From "The Art of Irish cooking" by Monica Sheridan