Preheat the oven to 350 degrees Fahrenheit and line an 8” x 8” or 9” x 9” square pan with parchment paper. 

Add all of the ingredients for the shortbread crust and topping to a large mixing bowl and mix until a thick dough forms. There's no need to separate the dry ingredients from the wet ingredients here. 

It’s perfectly normal for this mixture to be slightly crumbly but if it seems overly dry (in other words, it won’t mix), you can add more melted oil or butter until it resembles a slightly drier version of regular cookie dough. Note: You can also use a food processor for this step as well.

Measure out ¾ cup of the crumble mixture and set it aside to use later as the crumb topping.

Transfer the remaining crust mixture to the bottom of the prepared pan and press it into an even layer. Poke the crust several times with a fork (to promote even baking) and bake for 15 to 18 minutes, or until the edges are just barely beginning to turn golden brown.

While the crust is baking, you can prepare the blueberry mixture.

Transfer all of the ingredients for the blueberry filling to a saucepan (fresh blueberries, lemon juice, gluten-free all-purpose flour, sweetener and salt). Stir well, cover, and heat over medium-high heat. The berries will begin to bubble and leach liquid after a few minutes. Use a fork or a potato masher to mash the berries to allow the juices to flow. Continue heating just until the berry mixture is thick yet still liquidy, about 3 to 5 minutes.

Once the crust is out of the oven, pour the blueberry mixture on top of the crust and spread it into an even layer.

Sprinkle the reserved remaining crumble mixture over the blueberry layer.

Place the baking dish back into the oven and bake for another 22 to 30 minutes, or until the blueberry filling is bubbly and the topping is slightly golden brown.

Remove the blueberry bars from the oven and allow them to cool for 15 minutes before transferring them to the refrigerator to cool completely.

Once the bars have cooled, pull up on the parchment paper to transfer them to a large cutting board.

Use a sharp knife to cut individual bars.

If you’d like to make the optional glaze, combine the powdered sugar and water (or lemon juice) in a small bowl and stir until a thick runny glaze forms.

Drizzle the bars with glaze, serve, and enjoy!

For an even more decadent dessert, serve the bars with a scoop of vanilla ice cream.