These are a Christmas institution as far as I'm concerned. I got the recipe out of the Washington Post about a decade ago and have been making them ever since. They're a little finicky but basically easy—very different and very pretty. Easy for people to eat, too, as they’re finger food. The recipe seems to be all over the place on the web, so I guess it doesn't belong to anyone in particular. There's been one problem with it in that the tarts have tended to stick to the pan, although I haven't had this problem with the other fillings I list. So I really recommend using mini muffin liners, making sure that they're the 1 1/2" size and not the 1 1/4" size. Sugar content for these is pretty low because they're so small. My best guess is that they have 6 grams per tart, which surprised me. So you could, in theory, have four of these and not go over 25 grams. But that's assuming that you're not loading up your plate at a party with lots of other treats. Everything counts! The recipe says, “Never be tempted to put more than three cranberries in each one cup; one berry too many can force a tiny fruit eruption. For some reason, this recipe does not work well in regular-size muffin tins or as a large tart.” So you will need to get a mini-muffin pan—it will have 24 cups, and will work best if it’s nonstick. (Actually, you need to buy several pans, as I discuss below. But if my saying that scares you off of this recipe, just buy one for now.)
Make pastry shells from the recipe on this page and preheat your oven to 350. There's no need to pre-bake the shells for this recipe.
Variation: You can use chopped apples instead of cranberries, adding some cinnamon or apple pie spice to the filling mixture. Bake for the same amount of time. I'm not posting this as a whole separate recipe since everything else remains the same.