• Preheat the oven to 350F. Line an 8-inch square baking pan with parchment paper and set aside.

For the filling:

• Add the blackberries, sugar and lemon juice to a saucepan over medium-low heat.
  3 Cups (346 g) Blackberries, ½ Cup (100 g) Sugar, 1 Tablespoon Lemon Juice
• Once the berries release their juices, mash about half of the blackberries with a potato masher.
• Make a slurry of cornstarch and water. Stir the starch slurry into the berries.
  1 ½ Tablespoons (12 g) Cornstarch, 1 ½ Tablespoons Water
• Cook until the juices are bubbling and thickened. Allow to bubble for 2-3 minutes while stirring.
• Remove from heat and set aside to cool while you prepare the crust.

For the crust:

• Add the gluten free flour, sugar, baking soda, salt, butter, vanilla extract and lemon zest to a food processor. Pulse the mixture until it comes together in a crumbly dough. It will seem too dry, but it is okay.
  1 ¾ Cups (259 g) Gluten Free Flour, ½ Cup (100 g) Sugar, ½ teaspoon Salt, ¼ teaspoon Baking Soda, 10 Tablespoons (141 g) Vegan Butter, 1 teaspoon Vanilla, 1 teaspoon Lemon Zest
• Add ⅔ of the dough mixture into the prepared baking pan. Press it into an even layer that covers the bottom of the pan.
• Spread the blackberry jam over the bottom crust.
• Crumble the remaining dough on top of the blackberries.
• Bake in the preheated oven for 45 minutes or until the filling is bubbling and the topping is barely browned.
• Allow the bars to cool completely before removing them from the pan.
• Carefully lift the bars from the pan using the parchment paper flaps. Dust with a little powdered sugar (optional) and slice.