Instructions

• Preheat the oven to 375F degrees. Line an 8x8 inch square baking pan with aluminium foil and grease with butter or shortening.
  
• In a medium bowl toss together the ingredients for the blueberry layer (blueberries, cornstarch, lemon zest, lemon juice & sugar). Put aside.
• In a separate large bowl whisk together the flour, 1/2 cup granulated sugar and the baking powder.
• Cut in the butter & egg yolk using a fork until the mixture is crumbly.
  
• Press about two thirds to three quarters of the mixture into the bottom of the prepared pan. Pour the blueberry mixture over top.
  
• To the rest of the flour mixture, stir in the brown sugar and remaining 1 tablespoon of granulated sugar.
• Crumble the remaining dough over the blueberry mixture using your hands to distribute on the top.
• Bake in the oven for about 45 minutes, until you see the blueberries bubbling and the crumble layer starting to turn golden.
  
• Allow to cool fully to room temperature and ideally put in the refrigerator to chill . Then lift the bars out of the pan using the aluminium foil overhang and cut into squares. I used a pizza cutter which worked well. I also let the bars warm to room temperature which really brings out the flavors.
  
• Enjoy!