In a medium saucepan combine gelatin, granulated sugar, and salt. Stir in milk and egg yolks. Cook and stir over medium heat until mixture thickens and just coats a metal spoon. Remove from heat; whisk in sour cream. Stir in lemon peel, lemon juice, and vanilla. Transfer to a large bowl. Cover surface with plastic wrap. Chill until mixture mounds (1-1/2 to 2 hours).
Meanwhile, place the strawberries and preserves in a food processor or blender. Cover and process or blend until smooth. Transfer mixture to a small saucepan. Stir in the water and cornstarch. Cook and stir over medium heat until thickened and bubbly. Cook and stir 2 minutes more. Remove from heat. Stir in corn syrup. Transfer to a small bowl. Cover surface with plastic wrap and set aside to cool.
Line the bottom and sides of a 9-inch springform pan with ladyfingers, arranging ladyfingers cut sides up. Press together to form an even crust; set aside.
In a large bowl beat 1-1/2 cups of the whipping cream with a whisk or electric mixer until soft peaks form. Fold into gelatin mixture; set aside.
Remove 1/4 cup of the strawberry mixture and set aside. Spoon remaining strawberry mixture into crust-lined pan. Top with gelatin mixture (pan will be full). Spoon small mounds of reserved strawberry mixture over top of gelatin mixture. Use a thin metal spatula to marble the top of the mixture. (Or, pull the spatula through each mound to resemble heart shapes.) Chill for 2 hours. Cover loosely. Chill for 2 to 24 hours more or until firm.
In a medium bowl beat remaining 1/2 cup whipping cream and powdered sugar with a whisk or electric mixer until stiff peaks form. Pipe on top of charlotte. Makes 12 servings.