SPOILERS! (No need to answer this anymore; I figured it out all by myself!)
How do I collect the golden truffle that's among the placeholder Truffles?
Viewing post in Hey Kids! This is Advertising! comments
Oohh, sorry, that one's not communicated super well TBH! Look for a coupon code in the "placeholder matching game" area to the left of the flavor quiz, and you should be able to use it in the promotional code area of the shopping cart after you add the golden truffle :)
And thanks so much for playing!