Soak the gelatin in ice water and rinse the sea lettuce under cold water.
Heat the sour cream, mix with the sea lettuce and mix into a fine purée in the blender.
Add the gelatin and pass through a fine sieve. Place on ice water.
Beat the whipped cream to soft peaks, add add a small portion of the cream to sea lettuce and gelatin mixture.
Mix to a homogeneous mass.