Heat a large frypan over medium heat. Add butter, and when melted, add leek and fennel and sauté until softened.
Add flour, stir through and cook for 1 minute.
Slowly add stock, stirring continuously, then simmer for 1 minute. Season with salt and pepper and place into a bowl in the fridge to chill.
Add salmon, peas, potato, lemon zest and dill, and mix through.
Cut out four 18cm circles from the pastry, gather the scraps of pastry and re-roll and cut out two more 18cm circles.
Divide the salmon filling between the pastry circles, brush the edges with water, fold in half, lift the seam on top and crimp to seal.
Place onto a baking paper lined oven tray, brush the pasties with beaten egg and score several times (to allow steam to escape when baking). Refrigerate for 30 minutes.
Preheat oven to 200°C. Bake pasties for 30-35 minutes or until golden.
Rest for 10 minutes before serving with tartare sauce on the side.
