Poach the haddock and salmon in seasoned milk with aromatics until cooked.
Flake the fish and mix haddock with potatoes, butter, onions, and anchovy essence.
Fold in the salmon, chopped eggs, parsley, and dill by hand.
Season to taste and add poaching milk if the mixture is dry.
Form into four patties, coat with flour, egg, and breadcrumbs, then chill for 120 minutes.
Pan-fry patties in butter for five minutes per side and keep warm.
Wilt the spinach in 15g of butter and roughly chop the leaves.
Reduce the fish stock by half, then stir in sorrel and cream.
Serve the fishcakes on top of the spinach and garnish with sorrel sauce.