Deep frying - taste difference in saturated vs. unsaturated oil
Fries cooked in animal fat will taste distinctly different than those fried in a neutral vegetable oil. They will be much richer in flavor and may make you weep with joy.

If you haven't had them, you must stop what you're doing and make some duck fat fries.

Here is a good recipe: http://hecooksshecooks.net/2009/03/duck-fat-french-fries/