Pre-heat the oven to 350 degrees F and grease an 8×8 pan (9×9 would work as well but may require a little less bake time). I like to line my pan with parchment paper as well for easy removal.

In a medium bowl, combine the blueberries, sugar, lemon juice, and corn starch. Stir until the cornstarch is mostly dissolved and set aside.

In a large bowl, mix together the rolled oats, flour, salt, baking powder, and brown sugar.

Add in the softened butter and vanilla and mix until fully combined. The mixture will seem a little dry but should hold together when pressed between your fingers. Having a few larger chunks left in the mixture is perfectly fine.

Set aside a heaping cup of the crumble mixture and pour the rest into your prepared pan. Press the mixture firmly into the pan. Top with the blueberries and then sprinkle the remaining crumble topping over the blueberries. Gently press the topping into the blueberries.

Bake for 40-45 minutes or until the top is a nice golden brown. Let cool completely before cutting into the bars. The cooling process really helps the blueberry layer to firm up. Place in the fridge to speed up the process. Slice and ENJOY!