500gskinlessboneless fresh cod or haddock, chopped into large chunks
3tablespoonsfresh tarragonleaves only, finely chopped, or use 2/3 tbsp dried tarragon
2medium avocadosfirm and not quite ripe, peeled, deseeded, cubed
Sea salt and plenty of white pepper
A good squeeze of lemon juice
Peel the potatoes and cut into quarters. Boil in salted water with the bay leaf. Drain well, add a splash of milk and mash until nice and smooth. Set aside.
Preheat the oven to 400 F/ 200 C/ gas mark 6. Place the fish pieces in a medium oven dish, season with salt and white pepper and scatter the avocado cubes on top.
While the potatoes are cooking prepare the SAUCE. In a medium saucepan melt the butter over a low heat, add the flour and whisk until the mixture is smooth. Add the milk, cream cheese, mustard, increase the heat and whisk until the mixture has thickened. Remove from the heat, season to taste, add the onion granules, tarragon, a good squeeze of the lemon juice, half the cheese and stir well to combine.
Pour the sauce over the fish and avocado (reserving about 3 tablespoons). Cover with a layer of mashed potatoes, drizzle with the remaining sauce, sprinkle with the rest of the cheese and bake for 40 minutes. Serve immediately.