SLOWLY MELT BUTTER IN HEAVY PAN over low heat with 4 fresh sage leaves or 1/2 teaspoon dried, and the sliced garlic. When garlic is golden brown, remove it, but continue to cook butter until light amber with a distinctly nutty aroma. Scoop foam off top as it rises so that you can see the color, then pour it through strainer lined with layer of cheesecloth. Meanwhile, bring 4 quarts water to boil. Add 1 tablespoon salt and potatoes. Cook 5 to 8 minutes or until potatoes are fairly tender, but just short of being done. Rinse them immediately with cool water and set them in colander to drain, but reserve cooking water for pasta. Chop or crumble remaining sage leaves. Heat half the brown butter in wide saute pan, add leeks, sage, half the minced garlic and red pepper flakes. Cook over medium-low heat until leeks are soft. Add cabbage, 1 teaspoon salt and a little water. It might be necessary to add cabbage in stages, letting some of it cook down before adding rest. Cover pan and simmer until cabbage is cooked. Add Parmesan cheese and season with plenty of freshly ground black pepper and salt, if needed, to make flavors bright and strong. Return reserved cooking water to boil, add pasta and partially cook it, leaving it a little chewier than you would want to eat. Drain in colander, return it to empty pan and toss with rest of butter, remaining minced garlic and potatoes. Season to taste with salt and pepper. Butter casserole and layer half the noodles, half the cabbage and most of sliced cheese. Shake casserole so that vegetables and cheese can slip in among noodles. Add rest of pasta and cheese and finish with layer of cabbage. At this point, dish can be refrigerated until ready to bake. Bake at 425F about 20 minutes or until hot throughout and cheese is melted. If casserole is cold when placed in oven, bake it covered 15 minutes, then remove cover and continue baking until heated through. Serve from baking dish.