Brown the beef, onion, and garlic in a little oil in a frying pan. Drain off any grease. Add the spaghetti sauce into the browned meat mixture. Mix well. In a separate bowl, mix the ricotta cheese, milk and egg. Beat until thoroughly mixed and smooth then mix in the mozzarella cheese and the grated cheese, so that all the cheeses are combined. Grease the slow cooker with some vegetable shortening on the bottom and sides. Put about 1/4 of the meat and sauce mixture in the bottom of the slow cooker. Put a layer of noodles on top of that (break or cut them if needed). Put about 1/3 of the cheese mixture on top of that. Then repeat with sauce, noodles, cheese for another two layers. Top with meat sauce. Cook on low for 4-6 hours or until noodles are tender.