Preheat the oven to Gas Mark 6, 200˚C, fan 180˚C. Heat the oil in a large frying pan, add the leek and cook for 5 minutes.
Add the chorizo and cook for another 5 minutes. Add the butter, allowing it to melt, then stir in the flour. Cook for 2 minutes then slowly pour in the milk, stirring constantly, and simmer until thickened. Season and stir in gherkins, capers, parsley and fish.
Divide the mixture between 2 individual pie dishes. Brush the rim of the dish with egg. Cut thin strips of pastry and stick around the edge, then brush the pastry edges with egg and place a sheet of pastry on top of each pie.
Brush the lids with egg, make a little hole in each to allow the steam to escape and bake in the oven for 20-25 minutes until golden brown.
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Freezing and defrosting guidelines
Once the dish has cooled completely, transfer it to an airtight, freezer-safe container, seal and freeze for up to 1-3 months. To serve, defrost thoroughly in the fridge overnight before reheating. Loosely cover with foil and bake until dish is thoroughly heated through. Reheat until piping hot.
For top tips on protecting you and your family when preparing raw meat and poultry, visit Food Safety in the Home and view the full Food safety at home video.