Prep the baking sheet: Heat the oven to 400°F (200°C). Line a baking sheet with parchment paper to prevent sticking and make cleanup easy.

Make the egg wash: Whisk the egg with 1 tablespoon of water or milk. Set aside with a pastry brush.

Unfold the puff pastry: Lightly flour your counter. Roll the pastry into a rectangle about 10 x 12 inches to even it out. Don’t press too hard—you want those layers.

Cut and fill: Slice the pastry into 6 rectangles. Spoon 1–1.5 tablespoons of jam onto one half of each rectangle, leaving a small border. Don’t overfill.

Seal and shape: Brush the edges around the jam with egg wash. Fold the pastry over to make a pocket and press edges to seal. Crimp with a fork for a neat look.

Vent and glaze: Cut 2–3 small slits on top of each pastry to vent steam. Brush tops with egg wash. If using sliced almonds or coarse sugar, sprinkle now.

Bake: Place on the prepared sheet and bake 14–18 minutes, until puffed and deep golden. Rotate the pan halfway for even browning.

Cool slightly: Let pastries rest 10 minutes on a rack so the jam sets a bit.

Make the glaze: Stir powdered sugar, 1 tablespoon milk, vanilla, and a pinch of salt. Add more milk a few drops at a time until it’s thick but pourable.

Finish: Drizzle glaze over warm (not hot) pastries. Add lemon zest if you like a bright touch. Serve warm or at room temperature.