Cook the pasta in plenty of salted water, not too soft, save some of the cooking water. Fry the bacon, add the minced meat and let it brown. Add the carrots, celery, leek and garlic and simmer for about 10 minutes over a low flame. Top up with enough pasta water to make a sauce (not too thin). Stir in tomato paste and cheese. Season the whole thing with salt, pepper and possibly paprika and mix with the cooked spaghetti.