Preheat oven to 200°C and line a tray with greaseproof paper.
Roll pastry and cut into 30 squares measuring 6cm.
Score a smaller square inside each border, leaving a 7.5mm edge.
Bake for 18-20 minutes until puffed and golden brown.
Cool on a wire rack and remove the central pastry squares.
Simmer haddock in 300ml milk, then let sit for 10 minutes in residual heat.
Drain and skin the haddock while reserving the cooking milk.
Infuse the milk with onion, bay leaves, and thyme for 10 minutes, then strain.
Melt butter, stir in 25g flour, and gradually add the infused milk to thicken.
Season the sauce, stir in crème fraîche, and allow to cool.
Split sauce and mix half with haddock, prawns, and chives.
Mix the remaining sauce with chicken, tarragon, and white wine.
Fill pastry cases and bake at 200°C for 8-10 minutes until bubbling.