Grate the raw potatoes into a bowl. Turn out onto a cloth and wring, catching the liquid. This will separate into a clear fluid with starch at the bottom. Pour off the fluid and scrape out the starch and mix with the grated and mashed potatoes. Sieve the dry ingredients and mix in along with the melted butter. Add a little milk if necessary to make a pliable dough. Knead lightly on a floured surface. Divide into four and form large, flat cakes. Mark each into quarters but do not cut right through, and bake on a griddle or in a heavy pan.