Directions

1. In the bowl of a stand mixer fitted with the paddle attachment, or in a large bowl, using a hand mixer, beat the butter and sugar until light and creamy. Add the egg yolk and blend until combined. Add the flour and salt and blend until combined. Turn out the dough, gather it together, and form into a disk. Keep covered with a slightly dampened towel as you work.
2. If making tiny tarts, set out twelve 1-by-2-inch molds. Pinch off pieces of dough the size of a walnut and press one into each mold. Place the mold(s) on a baking sheet. Alternatively, press the dough over the bottom and up the sides of a 9-inch tart pan with a removable bottom. Chill the crust for 30 minutes.
3. Preheat the oven to 350° F.
4. Prick the crust all over with a fork. This will keep the crust from ballooning up in the oven, although it still may rise a bit; don’t worry, it will go back down. Bake tartlets for 8 to 12 minutes, 15 to 20 minutes if using a tart pan, until the crust is very lightly browned, about the color of sand. Watch carefully and do not overbake. Remove to a rack and cool completely.
5. Using a toothpick, carefully release the tiny tart shells from the pans; or, remove the large tart shell from its pan. Warm the jam in a small saucepan and spoon it into the baked shells. Let the tarts cool before serving.
6. Jam tarts are best when enjoyed within 3 days.