Duck fat makes for a special treat; you can also use clarified butter or ghee, available at specialty foods stores. (epicurious.com)
It is often sold in plastic 8 ounce (240 ml) tubs and can be found in specialty food stores and in the deli section of grocery stores. (joyofbaking.com)
I have never seen that at my grocery store (maybe I need to try some kind of specialty food store...)? (acouplecooks.com)