Add the butter and olive oil to a large pot on your stove top, and cook on low to medium heat until melted.
Add the sliced leek and bay leaves and sauté until translucent. Then, add the garlic and white wine and simmer for around 4-5 minutes to cook of the alcohol and raw taste.
To make a roux (to thicken the sauce), add plain flour to a small bowl. Mix together your stock cube and water, and add this to the flour, whisking until any lumps are gone. Add the roux to your leek mix and stir on a medium heat for 3-4 minutes, to cook off the flour.
Next, add the milk and mustard, and stir vigorously until the sauce base is thick enough to coat a spoon. Pour in your parmesan and tasty cheese and stir until the cheese is melted. Turn the heat off, then add in your pepper, chives and parsley. Set aside to cool. Add seafood when the mixture is room temperature or you are ready to cook your dinner
Note: While the sauce can be popped in the fridge if cooked in advance, just make sure to add 15-20 mins to the cooking time if it's cold when going in the oven.
Set your oven to 200 C (400 F) and grab your puffy pastry out of the freezer to de-thaw.
Choose two small pie dishes or one medium size one, and portion out your filling evenly.
Working fast, trim each pastry sheet so it will cover the top of your pie dish without too much overhang.
Place the pastry sheets over the pies, and scrunch the sides so they fit snugly. Brush your egg wash over the pastry, place dishes on a baking tray (in case there's any dripping!) and pop in the oven for around 16-20 minutes, until the pastry is golden.
Allow to cool slightly before serving with a side of buttered minty peas (or polenta chips!).