• Preheat the oven to 325 F. Line 9x13 inches baking pan with parchmentpaper and set aside.

Making the crust

• In amedium bowl, whisk together the dry ingredients for the crust (flour, oat,baking powder, salt) and set aside.
• In a separate bowl, using a hand mixer or in the bowl ofstand mixer, cream together butter and the brown sugar until well combined.  Add the egg yolk and the vanilla extract andmix to combine.
• Turn the mixer to low and add the dry ingredients and mixed untilcombined

  Pour the mixture into the prepared baking pan and press themixture firmly into the bottom of the pan evenly.

  Bake in the preheated oven for 15 minutes.

Making the blueberry filling

• While the crust is baking, prepare the blueberry filling by combining the blueberries, orange juice, zest, granulated sugar, and corn starch in a medium bowl. stir together and set aside.

Making the crumble topping

• In another medium bowl, stir together the ingredients for the topping (flour, brown sugar, melted unsalted butter, cinnamon, and salt)with a spatula. it should be crumbly or looks like breadcrumbs and set aside.

Putting it all together

• After the crust is done baking, bring it out of the oven and be careful because it will be hot.

  Pour the blueberry filling on the crust while it is hot and make sure the filling cover the crust evenly.

  Sprinkle the crumble toppings over the blueberry layer.
• Take it back to the oven and bake for 40 – 45minutes or until the topping turns golden brown and the blueberry filling is bubbling underneath the topping.

  Bring it out of the oven and allow to cool completely on a cooling rack for about 30 minutes before cutting into bars.

  Serve and enjoy.