The clams and cream can be made early in the day and refrigerated.
To make the lemon garnish, peel a lemon with a sharp knife, removing all the bitter white pith. Cut in between the membranes to release the sections into a bowl. Squeeze the membranes to extract the juice. Use the juice in the recipe and then cut a few of the sections into tiny triangles.
This dish can also be made without the caviar, using medium mussels in place of the clams.