Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper.

In a medium skillet, heat 1 teaspoon of olive oil over medium heat and sauté the sliced leek for 3-4 minutes until soft. Season with salt and pepper, then remove from heat.

Lightly flour a clean surface, roll out the puff pastry sheet into two equal rectangles.

Spread a thin layer of Dijon mustard on each pastry rectangle, place one salmon fillet in the center, and top with sautéed leeks.

Fold the pastry over the salmon and seal the edges firmly; brush with the beaten egg.

Place the parcels on the baking sheet and bake for 20–25 minutes until golden brown.

Let cool for 2–3 minutes before serving with lemon wedges and sides.