• Preheat your oven to 375℉. Line a 9x13-inch tray with parchment paper.
• Wash your blueberries and pat dry and set aside.
• In a large mixing bowl, add the flour, brown sugar, granulated sugar, baking powder and salt in a large mixing bowl and whisk together. Set aside.
  3 cups all-purpose flour, 1/2 cup brown sugar, 1/2 cup granulated sugar, 1 tsp baking powder, 1/2 tsp salt
• In a separate bowl, whisk together the egg and vanilla extract.
  1 tsp vanilla extract, 1 egg, room temperature
• Add the butter into the dry ingredients. Use forks, a pastry cutter or your hands to bring the mixture together until it looks like large crumbs. Add the egg mixture and whisk together, or use your hands! Stop mixing when the dough looks like large crumbs. Don't kneed to knead the dough into a firm ball.
  1 cup unsalted butter, room temperature, cut into 1 tbsp sized cubes
• Press a little more than half of the dough into the baking tray. Make sure to press it evenly and into the corners. It will thin, so make sure the dough is pressed evenly. Bake for 5 minutes.

Blueberry Filling

• In a mixing bowl, whisk together the remaining 1/2 cup granulated sugar, lemon juice and cornstarch. Add blueberries to the bowl and toss them to evenly coat them.
  4 cups fresh blueberries (or frozen blueberries that are thawed and patted dry), 1/2 cup granulated sugar, 2 tbsp lemon juice, 1 tbsp cornstarch
• Pour the blueberry mixture over the warm cookie dough, making sure to spread it out evenly.
• Take the leftover cookie dough and sprinkle it over the blueberries. Crumble any bigger pieces in-between your hands.
• Bake for 35 - 40 minutes until the top looks golden brown and the filling is slightly bubbling.
• Cool the bars for 1-2 hours before cutting into 15 medium sized bars.