Open the oysters and pour away the juice. Take a small pan and add the egg yolk and champagne and whisk the mixture into a foam over a low heat until you have a sabayon that does not collapse. Finely chop the shallot and press the garlic in a garlic press. Wash the spinach and leave to drain in a colander. Fry the shallot and garlic in a pan and braise the spinach with butter. Leave the braised spinach to drain on kitchen paper or a kitchen towel and squeeze out the remaining liquid. Put a little of the spinach in the oyster and add the foamy sabayon next to the spinach.
