From the NY Times http://www.nytimes.com/2015/08/02/magazine/the-miracle-of-preserves.html

Remove the peel from four grapefruits with a knife.

Slice three thinly.

Segment the fruit itself from its membrane into a bowl, with all attendant juices (remove pits, or did I have to mention that?).

Boil the sliced peel with 2 cups of water for 20 minutes.

Add grapefruit, juice and three cups of sugar, and boil until it lightly jells.

The result is bitterer than orange marmalade, a perfect expression of grapefruit’s oddities and opposites.