Oysters au gratin with champagne sabayon

Preparation

• 1 Open the oysters neatly, carefully detach them from their shells and store the oyster meat separately from the shells in a container. Catch the oyster liquid and keep it separate. Pour the rest from the tray over the oysters.
• 2 Put the champagne and tarragon in a small saucepan and bring to the boil. Leave to soak for 3 minutes on low heat, then sieve.
• 3 Put this champagne liquid together with the oyster liquid and the egg yolks in a bowl au bainmarie. Beat with a whisk until everything is well mixed.
• 4 Now beat the clarified butter through it, stirring it quickly in drops. Season to taste with lemon juice, pepper and salt.
• 5 Heat the oysters very gently in a small saucepan in their own liquid for 1 minute.
• 6 Put the oysters back in the shell, in the deep side. Pour a little champagne sabayon over each oyster so that they are all completely covered. Grate the oysters briefly under a hot oven grill and serve on a platter, placing the oyster on the back of the remaining oyster shell to keep them upright.
• 7 Au bain­marie
  With this method, you increase the temperature slowly so that the different components can bind well. You put a pan with a layer of water on the fire until it boils. Hold it at boiling point and hang on the edge of the pan a bowl containing the ingredients, so that the bowl hangs above the water but does not touch the water. It is the steam of the boiling water that heats the contents of the bowl.