Luxury fishcakes with tartare velouté

Name: Luxury fishcakes with tartare velouté
Ingredients: 1 large red-skin potato (about 250g); 250g smoked cod or haddock; 250g hake; 2 bay leaves; 1 tbsp English mustard; 500ml milk; 1 egg yolk, plus 2 eggs, beaten; 25g butter; 1 whole nutmeg, for grating; ½ lemon, zested and juiced; 100g mature cheddar, grated; 100g mixed white and brown crabmeat; 2 bunches of spring onions, finely chopped; 100g plain flour; 100g panko breadcrumbs; 4 tbsp sunflower oil, for frying; poached eggs, lemon wedges and pea shoots, to serve; 25g plain flour; 50ml double cream; squeeze of lemon; large handful parsley leaves, chopped; 2 tbsp capers, chopped