Prepare the crust: Preheat the oven to 325°F (163°C). Mix the graham cracker crumbs, sugar, and melted butter. Press into the bottom of an 8x8-inch baking dish lined with parchment paper. Bake for 8-10 minutes, then let it cool.
Make the cheesecake layer: In a bowl, beat the cream cheese and sugar until smooth. Add cornstarch and mix until combined. Beat in the egg, followed by the sour cream and vanilla, mixing until smooth. Pour the batter over the cooled crust.
Make the strawberry swirl: In a saucepan over medium heat, cook the strawberries and sugar until they break down. Dissolve the cornstarch in water, add to the saucepan, and stir until the mixture thickens. Strain to remove seeds, then let it cool slightly.
Create the swirl: Drop spoonfuls of the strawberry sauce onto the cheesecake batter. Use a toothpick or knife to swirl the sauce into the batter. Sprinkle diced strawberries on top.
Bake: Bake at 325°F (163°C) for 30-35 minutes, or until the edges are set but the center is slightly jiggly. Let the cheesecake bars cool at room temperature, then refrigerate for at least 4 hours before slicing.
Make the whipped cream cheese frosting: Beat the cold cream cheese and powdered sugar until smooth. Gradually add heavy cream while mixing, then add vanilla. Beat until stiff peaks form. Pipe or spread onto the chilled cheesecake bars before serving.
