Prepare the dough: Preheat the oven to 375 degrees. Place the flour in a bowl with the salt, sugar, and cut the butter into small pieces. Work the flour and butter together with your hands, until the mixture is well blended. Sprinkle the water over the mixture to smooth out the any small irregular clumps. Work the dough vigorously until it is relatively smooth. You may also use a food processor, if desired. Wrap in plastic and let the dough rest 30 minutes.

Shape the tarts: Roll out the tart dough on a cold lightly floured surface. The dough should be about 1/8″ inch thick. Cut rolled out dough into 3″ by 5″ shapes, using a postcard as a visual gauge. (For smaller tarts, simply use a smaller measurement.) Cut 8 rectangles, and use a pastry scraper to place 4 bottoms onto cookie sheet lined with parchment. Place 2 to 3 tablespoons of jam onto the center of each pastry of the 4 bottoms. Place the 4 pastry tops onto the jam centers, aligning the corners. Press the edges with a fork, until each tart is closed, working around the entire rectangle. (These may be prepared ahead of time and refrigerated or frozen.)

Bake and serve: Bake for 25 minutes, or until the tarts are golden brown. Serve immediately with a sprinkling of powdered sugar.