Every time you cook duck you can render out the left over fat and save this for many delicious uses
This fat can be stored in the fridge for a long period of time if done correctly.
Method
After roasting a duck or frying breasts or legs, take the meat out from the dish or pan and pour out all the liquid into a heat proof clear container.
Refrigerate it until it solidifies.
Tip or scrape out the white fat, ensuring that you scrape off all the water soluble layer that has accumulated at the bottom and any non-fat bits that have risen to the top of the fat.
If there is any water soluble product remaining in the fat, it will increase the level of oxidation and decrease the lifetime of the fat. So make sure to be conservative and keep only the fat taken from the middle leaving a barrier to the top and bottom waste.
This will leave only white hard fat, delicious to use for roasting potatoes or a multitude of other vegetables!