Three-Fruit Marmalade

The archetypal orange marmalade is made with bitter Seville oranges, which are available only for a short time in midwinter. Try this variation, in which refreshing grapefruit and lemons play off the sweetness of oranges, creating a marmalade with nuanced, complex citrus flavor.

Steps

1. Wash the fruit under cold water and dry it with towels. Slice each fruit in half lengthwise and then crosswise into very thin half-moons. (Do this on a plate or flexible plastic cutting board so you can save any juices that accumulate.) Discard the seeds and the core of the grapefruit.
2. Measure the lightly packed fruit and reserved juice in a liquid measure. Put fruit and juice into a large pot and add two times as much cold water. Bring to a boil and then simmer gently, covered, for 2 hours. Uncover and let sit overnight.
3. The next day, measure the fruit and liquid. Add an equal amount (by volume) of sugar. Cook mixture in 3 or 4 batches over high heat in a heavy-bottomed pot. Stir marmalade frequently until it reaches the jellying point. Test by putting a small amount on a plate in the freezer; it should gel when cool.
4. While the jam is cooking, sterilize 6 pint jars: Set them right-side-up on a canning rack, cover with hot (not boiling) water to a depth of one inch, boil for 10 minutes, drain, and hold in a warm place, such as a low oven, until ready to fill with jam. (Clean the lids and ring bands with hot, soapy water, then let them soak in hot water until needed.)
5. Pour the hot marmalade into the hot, sterilized jars. Cover with the clean lids and ring bands and let sit on dishtowels until the lids seal, then tighten the ring bands and allow to finish cooling.