2 tbsp olive oil
2 onions, sliced into rings
750g waxy potatoes, peeled and sliced
500g tomatoes, sliced
600g white fish fillets, cut into large chunks
1 sprig of fresh thyme
1 bay leaf
200ml fish stock
salt and freshly ground black pepper
fresh thyme to garnish

Heat 1 tbsp of the oil in a large flameproof casserole dish and cook the onions gently until transparent. Lift out half and set aside. Remove the casserole from the heat.
Place a layer of potato slices on top of the onions in the casserole, followed by a layer of tomatoes, then fish, then the remaining onions. Repeat until the ingredients are used up, finishing with a layer of potatoes. Season each layer with salt and pepper and place the thyme and bay leaf on top.
Pour over the fish stock and add the rest of the oil. Put the casserole back on the heat and bring to the boil. Reduce the heat, cover, and simmer for 40 minutes or until the fish and potatoes are tender. Garnish with fresh thyme.