Whip the cream until it forms soft peaks. Fold in the horseradish. Spread each quarter of bread with some of this mixture.
Top the whipped cream with a thin slice of smoked salmon.
Top each slice of salmon with a dab of sour cream, and then sprinkle a little caviar over the sour cream, pressing down lightly so it will stay in place.
Tuck a tiny sprig of parsley or dill i