Preheat the oven to 375 degrees then spray a 9x13” baking pan with nonstick spray and set aside.

For the blueberry filling: To a medium-sized mixing bowl add the blueberries, sugar, gluten free flour blend, lemon zest, the juice of ½ lemon, and vanilla then fold with a spatula to combine. Set aside.

For the crust: To a large mixing bowl add the gluten free flour blend, granulated sugar, brown sugar, baking powder, cinnamon, and salt then whisk to combine.

To a small bowl add the egg and vanilla then whisk with a fork to combine. Drizzle over the flour mixture then stir with the fork until incorporated. Add the cold, cubed butter then use a pastry cutter or your fingertips to blend the cold butter completely into the flour mixture until the texture is like sand. A handful of the mixture should hold together when squeezed inside your fist.

Scoop a little more than half the crust mixture into the prepared baking pan then press down firmly with the bottom of a measuring cup or glass to create an even layer. Pour the blueberry mixture over the top then spread into an even layer. Squeeze handfuls of the remaining crust mixture into clumps with your hands then crumble evenly over the blueberry filling.

Bake for 38-40 minutes or until the top is golden brown, rotating the baking pan 180 degrees halfway through. Check on the bars at the halfway mark — if the top is browning too quickly, place a piece of foil on top of the baking dish — no need to crimp. Remove the foil for the last 10 minutes of baking time so the top becomes golden brown.

Cool bars completely then let sit for at least 12 hours before slicing and serving. Store in the refrigerator for up to three days, or freeze for up to 6 months. Thaw in the refrigerator.