Sift thoroughly together flour, salt, sugar and baking powder.
Rub in potato.
Add sufficient liquid to mix rapidly and smoothly into soft dough. This will require about one pint of liquid.
Turn at once into greased loaf pan, smooth top with knife dipped in melted butter, and allow to stand in warm place about 30 minutes.
Bake in moderate oven about one hour.
When done take from pan, moisten top slightly with cold water and allow to cool before putting away.