Winter on the East Coast can be (and thanks to this short-lived cold snap, still is) a bit dreary. Apples & pears, harvested back in October and November, have been cellared, and while some varieties may be awesome, most will be reaching the end of the operational awesomeness, their sugars converting to starches and the structure giving way to mealier, grainier textures. Most stone fruits and related crops are still a while off, and numerous warm snaps may have lead to early budding which, followed by a return to cold weather, may decrease yields of cherries and other fruits this year. In other words, we still have many weeks before we can access any solid local fruits (let alone salad greens and, dare i say it, tomatoes).
Traditionally, the East Coast has received a respite from the winter fruit doldrums through the world of citrus; in the 1700's, it was sour oranges from Spain, sweet oranges and lemons from Italy and the Ottoman provinces, and limes from the Afro-Caribbean, and in the late 1800's, by icebox rail from California. Representative of plenty and richness in the New Year, oranges became occasional Christmas gifts (ever get one in a stocking?) and a generally active presence on middle-class tables during the winter season. (Jared Farmer, in his "Trees in Paradise: A California History", gives an awesome evaluation of American culinary and consumer preferences on the citrus.) The citrus club has only grown, as Texas and Florida jumped into the commercial game in the 1940's, and the Citrus Variety Collection at UC Riverside began to develop new cultivars and dig into the multiplicity of global varieties of citrus from blood oranges to Australian finger limes (mostly for geekiness, but also to keep the diversity of California commercial citrus crops highly competitive on the global market).
The Cara Cara, by all rights, shouldn't exist. It's a spontaneous hybrid, a mutation derived from the Bahia Navel (itself a grafted cross between a Portuguese Sour and Valencia Sweet oranges) that found it's way to California in the 1980's. In this particular mutation, the fruit produces elevated levels of lycopene, a cartenoid that gives red grapefruit and blood oranges their deep hues and berry-like flavors (and tomatoes their deeply-hued flesh). The result is a navel orange with grapefruit-like qualities of slightly pinkish, juicy-sweet and bracingly bitter flesh with a firm, almost cinnamon-spicy zest. While a great eating orange, it also has a multitude of culinary applications -- think in salads with avocado and pickled red onion, or mixed with other citrus into a raw compote for savory (ceviche) or sweet (tossed over pound cake and whipped cream).
I have to believe that's part of the reason the marmalade itself is so versatile. It doesn't have the aggressive, almost tannic bitterness that a three-fruit marmalade would have, nor the cloying sweet-sourness that tends to come along for the ride. We've been taking samples and trying them out and thus far the marmalade itself lends to sweet dishes on its own -- toast, ice cream, the great Provençal dish of marmalade omelette with fresh chevre -- but diluted down by stock or as a component of a sauce, the endless dressing or savory uses of the marmalade could be legion. Duck l'orange comes to mind immediately, but dishes where bitter orange is used, like in some Persian, Moroccan, and Iraqi dishes (think braised lamb with cooked citrus juices and couscous) and a whole world opens up. It's a definite example of the way in which cultivar-specific cooking can be manifest -- we couldn't have necessarily done this with, say, Valencia oranges or generic navels; even Ruby Red grapefruit would have been too bitter, and the pigment dulls too much. The use of the Cara Cara was purposeful, intentional, and as a result, we get to offer you something a little more dynamic than you'd find on your average store shelf.