Creating this delightful Blueberry Jamboree is straightforward when you follow these steps:

1. Preheat the Oven: Set your oven to 350°F (175°C).
2. Prepare Berries: Rinse the blueberries thoroughly and drain. In a mixing bowl, combine the blueberries, granulated sugar, lemon juice, cornstarch, and vanilla extract. Toss gently until the blueberries are evenly coated.
3. Cook Blueberries: Transfer the blueberry mixture into a saucepan over medium heat. Cook until the juice begins to bubble and the mixture thickens slightly, about 5-7 minutes. Remove from heat and let it cool.
4. Make Whipped Cream: In a separate bowl, add the heavy whipping cream, powdered sugar, and vanilla extract. Using an electric mixer, beat the mixture until stiff peaks form.
5. Prepare the Base: If using store-bought shortcakes, place them on a serving platter. If using homemade sponge cake, slice it into layers and place at the bottom.
6. Layer Blueberries: Spoon the cooled blueberry mixture over the base, ensuring it is evenly distributed.
7. Top with Whipped Cream: Spread the whipped cream generously over the blueberry layer, covering it completely.
8. Set and Cool: Place the assembled Blueberry Jamboree in the refrigerator to cool for at least 15-20 minutes before serving.
9. Garnish (Optional): Before serving, you can top it with additional blueberries or mint leaves for a beautiful presentation.

By following these steps, you will create a dessert that is as rewarding to present as it is to eat!