Preheat oven to 350 degrees F. In a standing electric mixer fitted with a paddle, cream the cream cheese, cornstarch, horseradish juice and salt. Add egg and heavy cream. When filling is mixed thoroughly add diced smoked salmon and fold it in. Place in buttered 8-inch springform pan and bake for 1 hour or until cheesecake sets up. Remove from oven and let cool to room temperature. Slice into 6 equal portions and serve with bagels and sliced onions.