Preheat your oven to 400°F (200°C).

In a medium saucepan, add a touch of oil or butter over medium heat. Once hot, add the sliced leeks and sauté for about 5 minutes until soft and translucent.

Add the salmon fillets to the leeks and cook for another 3-4 minutes, breaking up the salmon into chunks. Season with salt, pepper, and dill.

Pour in the heavy cream and lemon juice, stir well, and let simmer for about 2-3 minutes until slightly thickened. Remove from heat.

Roll out the thawed puff pastry on a lightly floured surface and cut it into rectangles or squares. Spoon the salmon and leek mixture onto each pastry piece, fold over the edges to seal.

Place the pastries on a lined baking tray, brush the tops with cream or milk, and bake for 15-20 minutes until puffed and golden.

Remove from the oven and allow to cool for a few moments before serving warm.