Celeriac & shellfish pie

1. Preheat the oven to 180°C, gas mark 4. Rest the pastry at room temperature for 10 minutes. Meanwhile, bring the shellfish stock to a simmer in a large, deep frying pan. Add the frozen scallops, prawns and fish pie mix, cover and bring back to a simmer, then remove from the heat and set aside for 2-3 minutes, until just defrosted but not quite cooked. Remove the fish and shellfish to a large plate with a slotted spoon.

2. To make the sauce, melt the butter in a large saucepan over a medium heat. Slowly mix in the flour until thickened. Gradually whisk in the reserved shellfish stock. Bring to a simmer, stirring over a low heat and cook for 1-2 minutes, until thick enough to coat the back of a spoon. Season generously, then stir in the tarragon, double cream and the frozen celeriac. Mix well and cook for 2-3 minutes until the celeriac has just defrosted.

3. Gently fold the fish and any resting juices into the celeriac mixture, then spoon into the bottom of a 2-litre ovenproof pie dish. Brush the edges of the dish with beaten egg, then place the pastry over the top. Press the edges down with a fork and make a small hole in the middle of the pastry for steam to escape.

4. Bake for 30-40 minutes, until the fish is opaque, the prawns are pink and opaque, and the pie is piping hot and golden on top and the filling bubbles up through the cracks in the pastry. Serve with minted peas.