1. Preheat oven to 350 degrees and line a 9×9 inch baking pan with parchment paper. Set aside.

2. To make the Shortbread Base whisk together flour, white sugar, brown sugar, baking powder, cinnamon, and salt. Add in the cold cubed butter and either use a pastry cutter, your hands, or two forks to cut the butter until pea-sized crumbs.

3. In a small bowl whisk together an egg, milk, and vanilla extract. Pour that into the dry mixture, and mix that until combined. If needed, you can use your hands to make it easier for the mixture to come together. Once combined, it should look something like cookie dough.

4. Evenly press the dough into the 9×9 baking pan lined with parchment paper. Set aside.

5. To make the Blueberry Filling, in a large bowl, mix the blueberries, white sugar, cornstarch, and lemon juice. Pour that mixture over the Shortbread Base and spread it out.

6. Lastly make the Crumble Topping. Mix together rolled oats, brown sugar, flour, melted butter, salt, and vanilla extract. Sprinkle that mixture over the blueberry filling.

7. Bake at 350 degrees for 45 minutes or until the bars are completely baked through. Remove from oven and let cool for 1 hour in the refrigerator before serving.

8. Slice, serve, and enjoy!