4 x 225g/8oz baking potatoes, well scrubbed
½ small lemon, finely grated zest only
15g/½oz fresh flatleaf parsley leaves, finely chopped
30g/1oz plain flour
salt and freshly ground black pepper
30g/1oz butter, cut into cubes
2–3 tbsp double cream (optional)
300ml/10fl oz milk (any type)
320²µ/11½´Ç³ú fish pie mixture (see Tip below)
300g/10½oz frozen peas