Method

1. To make the sauce, combine the white wine vinegar, white wine, shallots, thyme, and bay leaf in a small saucepan. Bring to a boil and boil hard until the volume of liquid has reduced by one-third. Gradually whisk in the diced butter a few lumps at a time. Remove from the heat. Season to taste with salt and pepper, then strain the sauce through a sieve. Stir in the chives and diced tomato. Set aside in a warm place until ready to serve.

2. Season the fish with salt and pepper and smear 1/2 teaspoon of butter over the skin of each fillet. Prepare a steamer with boiling water. Set the fish in it, cover and cook for 4-6 minutes, depending on the thickness of the fish.

3. Meanwhile, to cook the spinach, melt the butter in a large frying pan. Add the garlic and cook for 1-2 minutes over a low heat without letting the garlic colour. Add the spinach and cook for a couple of minutes, stirring constantly until the leaves have wilted. Remove from the heat and season to taste with salt and pepper.

4. To serve, place the spinach on serving plates. Set the fish on the spinach and pour the sauce over the fish.