Line a greased biscuit-pan with some of the coffee cake dough. Roll the dough thin and let it come up on the sides of the pan, then set aside to rise. When risen, cut the prunes in halves (they must be the fresh ones, not dried), lay in rows thickly and close together all over the bottom of the pan, do not leave any space between the prunes. Sprinkle very thickly with sugar, lightly with cinnamon, and lay bits of fresh butter all over the top. Bake until done in a moderately hot oven.