For the Pretzel Crust:

1. Preheat your oven to 350°F (175°C). Grease or line a 9×13-inch baking dish with parchment paper.

2. In a large mixing bowl, combine the crushed pretzels, brown sugar, and flour.

3. Add the melted butter and vanilla extract to the dry ingredients, mixing until everything is well combined.

4. Press the mixture evenly into the bottom of the prepared baking dish.

5. Bake for 8-10 minutes, or until the crust is golden brown. Remove from the oven and allow to cool completely.

For the Blackberry Topping:

1. In a medium saucepan, combine the fresh blackberries, granulated sugar, lemon juice, and cornstarch. Stir gently to combine.

2. Cook over medium heat for 5-7 minutes, stirring occasionally, until the mixture thickens and the blackberries start to break down.

3. Remove from heat and let it cool to room temperature before spreading it over the cream cheese mixture.

For the Cream Cheese Mixture:

1. In a large bowl, beat the cream cheese with an electric mixer until smooth and creamy.

2. Add the powdered sugar and continue to beat until fully combined and smooth.

3. Gently fold in the Cool Whip, mixing until the mixture is light and fluffy.

4. Spread the cream cheese mixture evenly over the cooled pretzel crust.

Assembly:

1. Once the cream cheese layer is spread, top it with the cooled blackberry topping.

2. Refrigerate for at least 2 hours to allow the dessert to set and the flavors to meld.