A popular Mexican fast food chain called Del Taco makes a creamy white sauce that they call their “secret sauce.” The secret sauce at Del Taco is made with soy oil, vinegar, an egg yolk, and buttermilk solids.
People who like the Del Taco chicken taco like to eat it with the secret creamy white sauce. There is no official recipe for this tasty sauce because it is a secret.
If a customer says the code words “go bold” while placing an order, the secret sauce can be added to any menu item. This special offer isn’t listed on the menu, so customers often have to ask the Del Taco staff to make sure they know about it.