Spray an 8x8 inch square baking pan with cooking spray, or line with parchment paper.
In a food processor, mix together the flour, granulated sugar, brown sugar, baking powder, cinnamon, allspice and salt.
Add the cubed butter and pulse until small crumbs form.
Add the egg, lemon zest, and vanilla and pulse to mix.
Divide the dough in half. Spread and lightly press one half of the dough into the prepared pan. It should be slightly crumbly but hold together when pressed.
In a separate bowl, gently mix together the blueberries, sugar, lemon juice and cornstarch.
Spread the blueberry mixture on top of the pressed crust.
Spread the remaining crumbs evenly on top of the blueberries and bake for 30 to 40 minutes or until the top is slightly brown.
Let cool completely before cutting. Serve with a scoop of vanilla ice cream.
Storage :Store for up to 5 days in an airtight container in the refrigerator or freeze for up to 6 months in a heavy-duty freezer bag. Be sure to use parchment paper between the bars if you layer them.Tips:
You do not need to use a food processor, but it does save you some prep time. If you don’t have a food processor, you can use a pastry cutter to incorporate the dough together.
We used an 8x8 inch square baking pan: A 9x9 inch pan can be used if needed. It will result in thinner bars and you will need to cook the bars for 5-10 minutes less than in an 8x8 inch pan.
Let the bars set for 1-2 hours after baking so that the berry layer can set sufficiently. If you cut it before then be prepared for a mess (though it will be a delicious mess)