Miso cod with mackerel and coriander broth

Name: Miso cod with mackerel and coriander broth
Ingredients: 1 tbsp caster sugar; 1 tbsp mirin; 2 tsp sake; 2 tbsp white miso paste; ½ tbsp Korean chilli bean paste; 2 x 200g/7oz pieces thick-cut cod fillets; 500ml/18fl oz dashi stock; 2cm/¾in piece fresh root ginger, peeled and sliced; 1 tbsp coriander seeds, crushed; 1 smoked mackerel fillet, skin and trim removed and kept; 1 tsp white miso paste; 2 tsp red miso paste; 3 spring onions, sliced; 100g/3½oz fresh edamame beans; micro coriander cress, to garnish