Luxe fish pie

Name: Luxe fish pie
Prep time: 45 min
Cook time: 1 h 10 min
Total time: 1 h 55 min
Cuisine: British
Ingredients: 500g thick white fish fillets, such as cod or haddock, unskinned; 500g thick salmon fillet unskinned; 300g smoked haddock (preferably undyed); 700ml full fat or semi-skimmed milk; 1 medium onion cut into thin wedges; 2 bay leaves; 75g butter; 75g plain flour; 140g young spinach leaves; 3 tbsp white wine or vermouth (optional); 0.5 small pack dill roughly chopped; 1 ½kg potatoes (ideally Maris Piper), cut into even-sized pieces; 50g butter; 100g mature cheddar coarsely grated; 300ml tub half-fat crème fraîche