In food processor, pulse flour, salt, and sugar until combined. Add butter and pulse until mixture resembles coarse crumbs. Add 4 tablespoons water; process just until dough forms (if dough doesn't form, add remaining 1 tablespoon water).

Divide dough in half. Shape each half into 5-inch round disks. Cover disks tightly with plastic wrap and chill for 1 hour.

Line rimmed baking sheet with parchment paper. Unwrap 1 dough disk. On lightly floured surface, roll out dough to 1/4-inch thick. Use large heart-shaped cookie cutter to cut dough. Transfer hearts to baking sheet. Re-roll scraps once to cut more hearts, if desired.

Spoon and spread scant tablespoon jam on top of each heart, leaving 1/2-inch border around edges. Unwrap second dough disk, roll out and cut into hearts. Place hearts on top of jam-topped hearts on baking sheet, gently pressing seam with fingers to seal.

Use fork tines to seal seams, then poke top of each heart 3 to 4 times. Cover hearts with plastic wrap and freeze 2 hours or up to 1 week.

Heat oven to 375 degrees F. Uncover hearts and bake 20 to 25 minutes until crust is baked through and lightly golden. Cool completely before icing.

To make icing, mix powdered sugar with 1 tablespoon milk and vanilla. Add remaining tablespoon milk if needed to make smooth but thick icing. Spread icing over fully cooled hearts, leaving 1/2-inch border around edges. Top with red and pink sprinkles, if desired. Let icing set at room temperature.