Make the Cookie Crust & Crumble Topping

1. Preheat your oven to 350°F (175°C). Line a 9×13-inch baking dish with parchment paper.
2. In a large bowl, cream together the butter, granulated sugar, and brown sugar until light and fluffy.
3. Add the egg and vanilla extract, mixing until smooth.
4. In a separate bowl, whisk together the flour, baking powder, and salt.
5. Gradually mix the dry ingredients into the wet ingredients until a soft dough forms.
6. Reserve 1 cup of dough for the crumble topping and set aside.
7. Press the remaining dough evenly into the prepared baking dish to form the crust. Bake for 10 minutes, then set aside to cool slightly.

Make the Blueberry Filling

8. In a saucepan over medium heat, combine the blueberries, sugar, cornstarch, lemon juice, and lemon zest.
9. Cook for 5–7 minutes, stirring frequently, until the mixture thickens. Remove from heat and stir in the vanilla extract.

Assemble & Bake

10. Spread the blueberry filling evenly over the par-baked crust.
11. Crumble the reserved dough evenly over the top.
12. Bake for 30–35 minutes, or until the crumble topping is golden brown.
13. Let cool completely before slicing into bars.

Serving & Storage

• Serve at room temperature or slightly warm.
• Store leftovers in an airtight container at room temperature for 2 days or in the fridge for up to 5 days.