Big mac Sauce is an item that can be spread on food items like pizza, burgers, salad, etc. To assemble the burgers, spread some Big Mac sauce over the bottom base. Top with some shredded lettuce, chopped onion, a slice of cheese, beef, and a few pickle slices. Top with the centre bun layer, and spread with Big Mac sauce, onion, lettuce, pickles, and more sauce. Top with burger lid to serve. You can buy the delicious Big Mac sauce UK from various online stores.