Mix the mashed potato with flour, whole eggs, milk and cream, and beat until smooth. Beat in the extra egg whites and seasonings. Pass through a sieve into a clean bowl. Put to one side to rest. Heat a griddle or skillet until evenly hot. Grease lightly.
Drop dessert spoons of the mixture onto a griddle - it should hold its shape. Put small pieces of smoked salmon on top and then a little more potato batter to enclose the filling. After about 1 minute when the underside is golden, flip over with a palette knife and cook on the other side.
Serve 4 or 5 per portion surrounded with a rosemary cream and with a few shreds of smoked salmon on top or a teaspoon of salmon caviar.