In the Mediterranean, aïoli is typically made in the simplest of ways: garlic emulsified with olive oil and a dash of — no egg, no lemon, no vinegar. But in the United States, there are fewer rules, and often more ingredients.

These days in the U.S. “aïoli” is virtually synonymous with mayonnaise and can include all of the above ingredients and more.

One particularly tending aïoli variety is made with truffle flavor, usually in the form of truffle oil, which often doesn’t have truffles in it at all.

Nonetheless, the rich truffle aroma and the creaminess of the aïoli is drawing customers to order it as a side for everything from French fries to mussels. More chefs are also incorporating versions of truffle aïoli into highly acidic dishes to balance them out.

According to market research firm Datassential, truffle aïoli is found on 1.7% of U.S. restaurant menus, a 22% increase over the past four years.

Click through the above gallery to learn more about truffle aïoli, and to see how one restaurant is using it on the menu.