Remember what movie this is from?
"Okay, here's your preparation stuff. You got your sliced tomatoes, shredded lettuce, secret sauce." "What's the secret sauce?" "Thousand Island Dressing. What's the secret sauce at Bronco Burger?" "Ketchup and mayonnaise."
Keep reading to see if you're right. Then, check out this video from McDonald's. One of their head chefs reveals the ingredients in the 'secret sauce' that's slathered on the Big Mac.