Preheat oven to 375° and right before adding crumb mixture, spray a 9 x 13 baking dish with a non stick spray.
In a medium mixing bowl, whisk sugar and corn starch together.
Add blueberries, zest from lemon and fresh lemon juice. Stir and let sit while making the crumb bars dough, stirring occasionally.
In a large mixing bowl, whisk flour, sugar, brown sugar, baking powder, salt and cinnamon together until combined.
Using a pastry blender or a fork, cut butter into flour mixture until crumbly.
In a small bowl, whisk egg and vanilla together and add to flour mixture once butter has been added and mixture is crumbly. Continue using pastry blender until combined.
Remove half of crumb mixture (approximately 3 cups) and press into prepared baking dish.
Stir blueberries and then add to the top of the crumb mixture.
With the remaining crumb mixture, squeeze with hands to combine as the crumb mixture is added over blueberries.
Place in the oven uncovered and bake for approximately 45 minutes or until crumb topping is slightly browned.
Let cool completely before cutting into squares.
Recipe adapted from Allrecipes.com