Mix flour, shortening, sugar, and salt together in a food processor until mixture resembles coarse crumbs. Add water and mix until a ball is formed. Refrigerate pastry until well chilled, at least 30 minutes.
Preheat the oven to 400 degrees F (200 degrees C). Grease 24 shallow muffin cups.
Roll pastry out thin; cut into rounds with a cookie cutter. Place each round in a muffin cup. Add 2 teaspoons of jam to each cup.
Bake in the preheated oven until golden brown, about 20 minutes. Cool tarts on a wire rack.
