The best salmon fish cakes

INGREDIENTS

• 450g floury potatoes , cut into chunks
• 350g salmon (about 3 fillets)
• 2 tsp tomato ketchup
• 1 tsp English mustard
• zest ½ lemon , plus wedges to serve
• 1 heaped tbsp chopped parsley
• 1 heaped tbsp chopped dill
• 3 tbsp plain flour
• 1 egg , beaten
• 100g dried breadcrumbs
• 4 tbsp sunflower oil
• salad , to serve