Wash the mussels and scrape with a knife; put them in a pot with chopped garlic, parsley, and pepper. Cover the pot and cook over high heat.

When the shells open, remove the pot from the heat, allow them to cool and remove the meat from the shells.

Strain the stock obtained from the shells through a cloth laid on a thick strainer and preserve.

Pour a glass of white wine and a spoonful of chopped red onion on the fire, let the sauce thicken; add one part of the mussels stock, let it cook until you get about half a glass of liquid.

Prepare the gelatin from the cube, leave to cool, and then add (always using a thick strainer) the liquid you were previously given.

Add a tube of ready-made mayonnaise, a spoonful of cream to the contents, and mix it all.

Add a little more mustard, lemon juice, and mix.

Pour this sauce as a base into 4 small glass cups, add the mussels and the rest of the sauce, and chopped parsley.

Garnish the cups with a few sprigs of parsley and place them in the fridge until the sauce thickens.