1 carrot, finely chopped
1 celery stick, finely chopped
1 garlic clove, roughly chopped
1 lemon, zest and juice
300g/10½oz baby new potatoes, halved
½ bunch flatleaf parsley, plus extra for garnish
½ shallot, finely chopped
1 thyme sprig
1 bay leaf
½ tsp peppercorns
100g/3½oz salted butter, softened, plus extra for cooking
2 x 125g/4½oz hake fillets
600g/1lb 5oz– 800g/1lb 12oz fresh mussels, debearded and scrubbed
250ml/9fl oz good-quality dry cider