Instructions: Pre-heat oven to 220c/gas 6. Skin fillet and very carefully remove all bones. Cut into 4 pieces. Wash fish and pat dry. Season with salt and pepper. Remove zest from lemons with a zester or fine grater. Peel and finely chop garlic. Mix lemon zest, chopped garlic and chervil in a bowl.

Put breadcrumbs into a frying pan and add olive oil, stirring and cooking until crumbs just bind together. Add lemon mixture to crumbs.

Press the crumb mixture firmly into the cod fillets and place the crumbed fillets on a baking sheet or in a shallow roasting tin. Roast in a pre-heated oven for 5-7 minutes until fish feels firm and crumbs are crispy and golden. Rest fish in a warm place for a few minutes.

Wash spinach leaves thoroughly while fish is cooking and shake dry. Heat a little olive oil in a large frying pan and quickly stir-fry spinach for seconds until the leaves wilt. Season very lightly with salt.

Serve cod on the spinach (or surrounded by it if in a dish) and with the lemon butter sauce.

Sauce: Peel and finely chop the shallot. Put into a wide shallow pan and pour in the wine vinegar and white wine. Reduce over a medium high heat to drive off the alcohol and excess acidity and to soften the shallot.

Take a piece of the zest off the lemon with a potato peeler and add it with the lemon juice to the pan. Add the sugar. Simmer together to blend all the flavours. Start whisking in the chilled butter a little at a time until the sauce is thickened to your taste, and glossy.

Season carefully then pass through a fine sieve into a clean pan and keep warm until ready to serve. Just before serving re-heat gently and strew with freshly chopped parsley or chives.

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