You can find fresh udon noodles in Asian markets and some supermarkets. They are usually packaged in portion-size bricks with accompanying soup base packets. If you can't find fresh udon, purchase dried udon noodles, then boil them and rinse in cold water before using in this recipe. Beef base is a highly concentrated form of stock. You can find it in paste or powdered form next to the bouillon in your grocery store.