2 tbspmild extra-virgin olive oil500 gmchat potatoes, very thinly sliced on a mandolin1½ fennel bulbs, thinly sliced on a mandolin, fronds reserved1small onion, thinly sliced2garlic cloves, finely chopped200 mldry white wine500 ml (2 cups)hot chicken stock4skinless blue-eye trevalla fillets (150gm each)½ cupcoarsely chopped flat-leaf parsleyFinely grated rind and juiceof 1½ lemons, plus lemon wedges to serve Saffron aïoli250 gmwhole-egg mayonnaiseJuiceof 1 lemon, or to taste½garlic clove, finely chopped¼ tspsaffron threads, soaked in 1 tsp hot water for 5 minutes
Heat oil in a large deep-sided frying pan over medium-high heat, add potato, fennel, onion and garlic and cook until fennel is just tender (4-5 minutes). Add wine, simmer until reduced by half (1-2 minutes), add stock, season to taste, bring to the boil, cover with a lid and cook until potato is almost tender (10-12 minutes). Top potato with fish, replace lid and cook until fish is just cooked through (4-5 minutes).
For saffron aïoli, combine ingredients in a bowl, season to taste and set aside.
Remove fish from pan and set aside. Stir parsley, lemon rind and juice and reserved fennel fronds into potato mixture and serve hot, topped with fish, with saffron aïoli and lemon wedges.