To be more specific, I use truffle oil. Regular truffles are not only difficult to find, but very expensive (I've had them in restaurants, and.... oh my!) Truffle oil is fairly expensive, but it goes a long way, it imparts a flavor that you can't get from anything else, and it is just..... lovely!
I use it in sauces and gravies and sometimes potato dishes etc. I buy my truffle oil at Williams and Sonoma and pay about $26.00 for a 4 oz (I think. I'm too lazy to go downstairs to look.) and it lasts about a year. You only need a few drops per pot of gravy or sauce. People exclaim and can't figure out what that wonderful flavor and aroma is!
I detest most mushrooms, but I love the flavor of truffles.
I once bought a more inexpensive brand at the grocery store and it was VILE. I ended up throwing it away. It tasted like mold.
This is the one I use.