For the cake: Preheat the oven to 350 degrees F. Beat the egg whites until frothy. Add the cream of tartar and beat until stiff. Sift the superfine sugar three times and add slowly to the egg whites.
Sift the cake flour and salt five times, and then fold slowly into the egg whites. Sprinkle in the vanilla and fold.
Bake for 35 to 45 minutes in an unbuttered angel food cake pan.
Set aside to cool completely, inverted on a bottle or jar that fits the cake pan.
For the filling: Dissolve the gelatin in boiling water and add the strawberries, stirring to break up and mix the berries.
For the icing: Whip the cream with the powdered sugar until thick.
To assemble: Place the cake, wide-side down, on a serving plate. Cut a 1-inch layer from the top and set it aside. Cut around the cake 1 inch from the outer edge to 1 inch from the bottom. Cut around the cake 1 inch from the inner edge to 1 inch from the bottom.
Gently remove the section of cake between the cuts and pour in the strawberry mixture.
Place the cake layer back on top and spread the icing all over the top and sides of the cake. Decorate with whole strawberries.