Mix the flour, baking-powder, salt and suet with sufficient water to make a soft, but firm, dough. Roll the dough into a rectangle about ¼ in. thick. Spread with jam almost to the edges, damp the edges and roll up lightly. Seal the edges. Put on to a well-greased baking sheet. Cook in a fairly hot oven (400° F., Gas 6) until cooked through: about 1 hr.