Step 1: Preheat the oven

Preheat your oven to 200°C (400°F).

Step 2: Sauté the leek

Melt the butter in an oven-safe skillet over medium heat. Add the sliced leek and cook for 5 minutes, stirring occasionally, until softened.

Step 3: Make the creamy sauce

Stir in the flour and cook for 1 minute to form a roux. Gradually whisk in the milk, followed by the double cream. Bring to a gentle simmer and cook for 2-3 minutes until thickened.

Step 4: Add the seafood

Stir in the Dijon mustard, lemon zest, and chopped dill. Add the salmon chunks and prawns, seasoning with salt and black pepper. Stir gently to coat the seafood in the sauce, then remove the pan from the heat.

Step 5: Add the pastry topping

Unroll the puff pastry and lay it over the skillet, tucking the edges around the filling. Brush the pastry with the beaten egg to ensure a golden crust.

Step 6: Bake the pie

Place the skillet in the preheated oven and bake for 20-25 minutes, or until the pastry is puffed and golden brown.

Step 7: Serve

Let the pie cool for a few minutes before serving. Scoop generous portions onto plates and enjoy!