Russ and I bought individual ones of these in Tasmania. This is my attempt to recreate them (and I think I got them better than right). I made 1 pie in an 8 inch pie dish using pre rolled sheets of short crust (which is how we get it in Australia).
Lay 1 sheet of pastry in pie dish, prick with a fork, cover with baking paper and then pour over a layer of dried beans, rice or lentils and bake in the oven for about 12 minutes. Remove, remove the foil and filling (and discard or save for your next pie.).
Meanwhile, melt the butter, add the diced onion and cook until softened but not coloured. Add the flour and cook, stirring for about a minute. Add the milk and whisk until smooth and thickened.
Remove from the heat and add in the lemon juice, salmon, brie, green onion, dill leaves and pepper (I tasted here and found it didn't need any salt).
Brush a little milk around the edge of the pastry bottom, pop on the top and trim to fit your pie dish. Brush more milk across the top. Prick a few holes in the top pastry to allow steam to escape.
Cook for 10 minutes at 200c then reduce the oven temp to 180c and cook a further 20 minutes or until golden brown.
We ate ours served with a leafy grean salad dressed with lemon infused olive oil and white wine vinegar.