Prepare the Crust (for pie or tart version)

1. Mix the Crust: In a medium bowl, combine the graham cracker crumbs, melted butter, and sugar. Stir until the crumbs are well-coated and the mixture holds together when pressed.
2. Form the Crust: Press the mixture into the bottom of a pie dish or tart pan, making sure to cover the bottom evenly. Use the back of a spoon to compact the crumbs.
3. Bake the Crust (optional): If you prefer a baked crust, preheat the oven to 350°F (175°C) and bake for about 10-12 minutes until golden. Let it cool completely before filling.

Prepare the Lemon Filling

1. Whisk Together Wet Ingredients: In a medium bowl, whisk together the lemon juice, lemon zest, sugar, eggs, melted butter, salt, and vanilla extract until smooth.
2. Pour into Crust: Pour the lemon mixture into the prepared (cooled) crust.
3. Bake the Filling: If you’re using a pie or tart, bake the lemon filling in the oven at 350°F (175°C) for 20-25 minutes, or until the filling is set but still slightly wobbly in the center. Let it cool completely, then refrigerate for at least 30 minutes to an hour.

Prepare the Blueberry Topping

1. Cook the Blueberries: In a small saucepan, combine the blueberries, sugar, and lemon juice. Cook over medium heat for 5-7 minutes until the blueberries start to burst and the mixture thickens slightly.
2. Cool the Topping: Let the blueberry topping cool completely before spooning it over the lemon filling.

Optional Whipped Cream

1. Make the Whipped Cream: In a mixing bowl, beat the heavy cream with powdered sugar and vanilla extract until stiff peaks form.
2. Serve with Topping: Spoon the whipped cream over the chilled lemon-blueberry dessert or serve it on the side.

Assemble the Dessert

1. Layer or Serve: Once the lemon filling is set and chilled, spread the blueberry topping evenly over the top.
2. Serve: Serve the dessert chilled, topped with whipped cream if desired.