Creating these scrumptious Blackberry Pistachio Dream Bars is a breeze when you follow these steps:

1. Preheat the Oven: Start by preheating your oven to 350°F (175°C). Line an 8×8-inch baking pan with parchment paper for easy removal.

2. Prepare the Base: In a mixing bowl, combine flour, rolled oats, brown sugar, granulated sugar, baking powder, and salt. Stir in the melted butter until mixture is crumbly.

3. Press into Pan: Pour the mixture into the lined baking pan, pressing it firmly into an even layer. Bake in the preheated oven for 15 minutes.

4. Make the Blackberry Layer: While the crust is baking, add blackberries, granulated sugar, cornstarch, and lemon juice to a small saucepan. Cook over medium heat, stirring gently until the mixture thickens, about 5-7 minutes.

5. Layering: After the base has baked, remove it from the oven. Pour the blackberry mixture evenly over the baked base to cover.

6. Prepare the Cream Cheese Topping: In a separate bowl, mix the softened cream cheese, powdered sugar, and vanilla extract until smooth.

7. Spread the Topping: Carefully dollop the cream cheese mixture over the blackberry layer, spreading it gently but evenly.

8. Add Pistachios: Sprinkle the chopped pistachios over the cream cheese layer for added crunch.

9. Bake Again: Return the pan to the oven and bake for an additional 15 minutes, or until the topping is set.

10. Cool Completely: Once baked, remove from the oven and let the bars cool in the pan on a wire rack for at least one hour. After cooling, refrigerate for another hour for easier slicing.

11. Slice and Serve: Once cooled completely, lift the bars from the pan using the parchment paper. Slice into squares and serve.