Big Mac Sauce isn't the same as Thousand Island Dressing, but you can use it in place of the sauce. When I started testing this recipe, I had Jeff go to McDonald's and ask for special sauce. They actually sell it in little containers! We tried all kinds of variations of ingredients, including French dressing which some people suggested, to get as close to what the Big Mac sauce tastes like as we could. While there are still some differences in taste, we were so pleased with how the recipe turned out that I left it alone. You can also use a Thousand Island dressing in place of the sauce in this recipe if you prefer.