Place a large pasta pot on the flame with 3 quarts water and 2 tablespoons salt. Add the potatoes and bring to a boil. Boil 7 minutes, until the potatoes are just fork soft, and add the cabbage. Cook 3 to 4 minutes and add the pasta. Return to boil and cook 3 to 4 minutes until pasta is firm and still chewy.
Meanwhile, in a 10 inch saute pan melt the butter until the foam subsides and add the leeks, garlic and sage and cook until softened, about 6 to 8 minutes, and set aside.
Butter an earthenware oven dish and preheat oven to 385 degrees F. Spoon one quarter of the pasta mixture into dish, followed by one quarter leek mixture and one quarter grated cheese. Continue until all ingredients are finished. Place in oven and bake 10 minutes. Remove and toss like salad and serve immediately in the same bowl.