Use a food processor (or mixer, or by hand) to mix together the flour, salt, and sugar.
Cut the butter into small pieces. Add to food processor and pulse until butter is evenly distributed.
Add the water to the crumby mixture and blend until the dough forms. Gather dough into a ball, place in bowl and cover. Place in the refrigerator for 30-45 minutes.
Roll out dough to a lightly floured surface to about 1/8" thickness. Cut into Pop-tart size rectangles. Half will serve as the top.
Spread about 3 tsp of jam to each of the rectangles (half of them), allowing space around the edges to seal them with a fork. Top with remaining rectangles. Seal edges using the tip of a fork. Poke some vent holes at the top (to ensure they don't explode).
Place in 350 F oven for 28-33 minutes, until golden. Allow to cool for for at least 40 minutes before applying icing.