1 large leek, very thinly sliced
1kg/2lb 4oz potatoes, peeled, cut into cubes and boiled
salt and freshly ground black pepper
1 tsp dried mixed herbs
150g/5½oz mature cheddar, grated
100²µ/3½´Ç³ú cream cheese
150ml/5fl oz full-fat milk, plus 1 tbsp for brushing
320²µ/11½´Ç³ú puff pastry sheet
freshly cooked frozen peas, to serve