To make the broth, heat 2 tbsp olive oil in a saucepan over a medium heat. Stir in the celery, shallots, garlic and chilli flakes. Cover and sweat for 3-4 minutes.
Add the tomatoes and wine and allow to simmer with the lid off for 5 minutes. Stir in the fish stock, olives and fennel. Season, reduce the heat and simmer for 30 minutes. Add the samphire, mint and dill for the final 4 minutes.
To make the gnocchi, put the potatoes (still in their skins) into a pan of salted boiling water and cook for 10-15 minutes, until tender. Drain and peel quickly. Pass through a sieve or a ricer into a bowl, then mix in the eggs, ⅔ of the flour and the dill. Stir, adding more flour, until the mixture comes together as a dough, working as little as possible so it doesn’t become tough.
Divide the dough into three equal pieces and roll each into a long log, dusting with a little flour if needed. Cut the logs into 3cm-long dumplings, pressing each dumpling against the back of a fork to create ridges.
Bring a pan of salted water to the boil and cook the gnocchi in batches, simmering for about 2 minutes or until they rise to the surface, then drain. Melt the butter in a large frying pan and toss in the gnocchi, then remove from the heat.
For the salsa verde, mix all the ingredients in a bowl.
Heat 2 tbsp olive oil in a large non-stick frying pan over a medium-high heat. Season the sea bass fillets and place them skin side down in the pan. Press down firmly with a fish slice and cook for 5 minutes, then flip and cook for a further 2 minutes on the flesh side.
To serve, spoon the broth into 4 warmed bowls. Dot some gnocchi around each, then top with the sea bass fillets. Add a spoonful of salsa verde and a lemon half to each, and sprinkle over any remaining herbs.