Rinse and select cress or possibly purslane. Bring plenty of water to the boil. Pour in cress or purslane and blanch for just 30 seconds. Drain, squeeze lightly, then chop finely.
Remove the coraille (red appendage on the muscle meat) from the mussels and rinse under cold water. Dry with kitchen roll. Cut very thick mussels in half horizontally. Coat both sides of the Coquilles St.Jacques with olive oil.
Remove the shell from the shallot and chop finely. Sauté in the butter until light yellow. Extinguish with the Noilly Prat. Add the fish stock and cook on high heat for about 5 minutes. Now add the heavy cream and the chopped cress and whisk until creamy.
Important: the soup must not make more, otherwise the cress will become bitter. Season with salt, pepper and lemon zest.
At the same time that you are finishing the soup, cook the Coquilles St.
Jacques in a coated frying pan without adding more fat, meanwhile, roast for 2-3 min not too hot. Season lightly with salt and season with pepper.
Arrange the soup in warmed plates and pour in the mussels. Bring to the table immediately.