Directions:

• Preheat the oven to 180C/350F/Gas 4. Line a large baking tray with baking parchment.
• Slice the cucumbers lengthways, scrape out the seeds with a teaspoon, and chop into 1cm/½in thick pieces. Place the cucumbers in a mixing bowl with the mustard, honey, vinegar and finely chopped dill. Season well with salt and freshly ground black pepper and set aside.
• Roll the pastry out to 40cm/16in x 30cm/12in on a lightly floured surface. Lay on the lined baking tray.
• Lay one fillet in the centre of the pastry, pile half of the filling on top and then cover with the second fillet.
• Brush the edges of the pastry with the mixture of milk and beaten egg. Fold the pastry over the fish, sealing the edges by pressing them together, leaving a gap in the centre, so that you can see inside. Brush the pastry with more beaten egg and milk and bake for 45 minutes.
• Serve with the remaining cucumber mixture.