1/8 t salt
3/4 c cold, unsalted butter, cut into small pieces
3-oz. cream cheese, chilled, cut into small pieces
1 1/2 t cider vinegar
5 medium (about 2 pounds total) firm cooking apples, such as gala or granny smith
1 t finely chopped lime or lemon zest
about 1 c cajeta, store-bought or homemade
the dough. in a food processor, combine the flour, baking powder, and 1/8 teaspoon of salt. pulse to mix thoroughly. add 4 ounces (1/2 cup) of the butter and all the cream cheese, then pulse 5 or 6 times until the mixture looks like coarse crumbs. drizzle the vinegar and 1 1/2 tablespoons of ice water over the dough and pulse 3 times to bring the mixture together into rough clumps. turn out onto your work surface, divide into 6 parts, and roll each into a ball. place the balls on a plate, cover with plastic wrap, and refrigerate for about 45 minutes.
the apple filling. peel and core the apples, then cut them into 1/2-inch cubes; you should have about 6 cups. in a large, heavy skillet, heat the remaining butter over medium-high. add the apples and stir nearly constantly as they cook, first releasing their juice, then softening and browning as the juice evaporates, 8-10 minutes. when the apples are soft and browned, add 1/2 teaspoon of the lime or lemon zest and 1/4 cup of the cajeta. stir for a minute or two, then remove from the heat. scoop the mixture onto a baking sheet to cool to room temperature, about 15 minutes.
forming the tarts. roll out each ball of dough into a 6-inch round. transfer the pastry rounds to a parchment-covered or lightly oiled baking sheet, leaving about 2 inches between them. if the apples haven't cooled by this point, cover the pastry with plastic wrap and refrigerate.
spoon 1/3 cup of the filling onto the center of each pastry round, leaving a 1 1/2-inch border all around. carefully fold the dough edges up over the filling toward the center, gently pleating the dough as necessary. if time allows, now place the baking sheet in the freezer for about 20 minutes.