The ultimate fish pie

Name: The ultimate fish pie
Ingredients: 1.5kg/3lb 5oz potatoes (such as King Edwards, Maris Piper or Estima); salt and white pepper; butter, to taste; 100g/3½oz grated gruyère cheese; 1 litre/1 pint 15fl oz fish stock; 4 tbsp dry vermouth; 1 onion, roughly chopped; 1 small bulb of fennel, cored and chopped; 1 small carrot, chopped; 1 small stick of celery, chopped; 1 bay leaf; pinch saffron; 750g/1lb 10oz white fish (such as haddock, cod or hake); 250g/9oz smoked haddock; 200g/7oz salmon; 120g/4oz raw prawns; 75g/2½oz unsalted butter; 75g/2½oz plain flour; 150ml/5fl oz full-fat milk; large handful parsley, finely chopped; 150ml/5fl oz double cream; butter, to grease the dish; 125g/4½oz leaf spinach; 4 hard-boiled eggs; 25g/1oz ciabatta crumbs; 25g/1oz grated parmesan cheese