In a large bowl, whisk together flour, sugar, and salt.
Cut in cold butter until the mixture resembles coarse crumbs.
Add ice water one tablespoon at a time until the dough comes together.
Divide into two discs, wrap, and chill for 30 minutes.
Preheat oven to 375°F (190°C).
Roll out dough on a lightly floured surface.
Cut into 16 equal rectangles.
Place 8 rectangles on a parchment-lined baking sheet.
Add about 1 tablespoon of jam to the center of each.
Leave a border around the edges.
Top with remaining dough rectangles.
Press edges with a fork to seal.
Poke small holes on top for steam to escape.
Brush tops with egg wash.
Bake for 22–25 minutes until golden brown.
Cool completely.
Whisk powdered sugar, milk, and vanilla until smooth.
Spread glaze over cooled pastries.
Add sprinkles if desired.
Allow glaze to set before serving.