Preheat the oven to 350 degrees. Line an 8 x 8 baking dish with foil. Set aside.

In a medium bowl combine the flour, oats, sugar, brown sugar, cinnamon, and salt. Mix well.

Add in the butter and mix until a crumble forms. Stir in the egg yolk.

Remove 1 cup of the crumble mixture from the bowl. Press the remaining mixture into the bottom of the prepared pan.

In a medium bowl toss the blueberries with the lemon juice, sugar, and cornstarch. Pour over top of the crust in the pan.

Sprinkle the remaining crumble on top of the blueberries.

Bake for 40-45 minutes or until the crumble is firm.

I like to put the broiler on for 1 minute to darken the crumble but this is optional.

Cool completely on a wire rack.

When ready to serve remove the bars from the pan using the foil. Cut into squares. Enjoy!