Puff pastry fish pie

Fish stock:

275g fish bones (stomachs and heads removed)

1 tbsp rapeseed oil

1 onion sliced

1 stick of celery sliced

1 small leek sliced

4 cloves garlic

½ tsp whole black peppercorns

3.5 litre water

Fabulous Fish Pie:

400ml milk

300g fresh fish, diced into bite-sized chunks (such as hake, monkfish, pollock, cod)

200g smoked fish, diced into bite-sized chunks (such as haddock, coley or pollock)

70g butter

1 leek diced

2 cloves of garlic, minced

70g plain flour

350ml warm fish stock

1tb Dijon mustard

1 tb chopped parsley

1tb chopped dill

1 lemon zested

For the topping:

1 x 320g sheet puff pastry

2 egg yolks beaten

Sea salt flakes