In a food processor, pulse together flour, salt and granulated sugar. Add butter and pulse mixture until resembles coarse meal (it won't really come together in pieces much at this point, so don't over-process, just pulse until butter is no longer in large pieces). Add 4 Tbsp water and pulse several times, if it doesn't come together in clumps add remaining 1 Tbsp water. Drop mixture onto a clean surface, gather dough into a ball then divide into two portions. Shape each portion into about a 5-inch disk. Cover each with plastic wrap and chill 1 hour.
Arrange 4 of the rectangles, spaced evenly apart on prepared baking sheet. Spread 1 1/2 Tbsp of jam evenly down the center of each rectangle, leaving about a 3/4-inch rim on all sides uncoated. Top each with another rectangle, then seal edges with your fingertips, then reseal with a fork. Poke the top center of each tart about 4 times with a toothpick. Cover and transfer to freezer to chill at least 2 hours or up to one week. Repeat process with remaining disk of dough.