Grease a 9x13 inch baking pan. Spoon some of the leek/cream sauce into the bottom of the pan. Follow with a layer of noodles, spread with some ricotta mixture. Sprinkle with parmesan. Lay some of the squash across this layer, and top with the cabbage, then another layer of leeks/cream, and another layer of noodles. Continue repeating, ending with a layer of noodles: top with ricotta, spoon the last of the cream sauce over it (at this point there should be no more leeks left in it), and sprinkle generously with parmesan. Finish with a dusting of black pepper.
Bake at 375 degrees for 25-30 minutes, until the cheese on top is golden. Bon appétit!