PREPARE THE BAKING PAN

1. Preheat oven to 350F.
2. Grease an 8×8 inch square metal baking pan and line with parchment paper, allowing the paper to hang over each side for easy removal. Set aside.

PREPARE THE CRUMBLE TOPPING & BASE

1. Combine the rolled oats, gluten-free 1:1 flour, almond flour, light brown sugar, granulated sugar, baking powder, cinnamon, and salt in a mixing bowl and whisk to combine.
2. Stir together the melted butter and vanilla extract and pour over the dry mixture. Stir together until all of the dry ingredients are fully coated with the butter and evenly combined.
3. Remove 3/4 c (lightly packed) of the crumble mixture and place in the refrigerator (this will be the topping).
4. Press the remaining crumble into the bottom of the baking pan. Then smooth the top and edges with an offset spatula to create an even, smooth layer.

PREPARE THE BLUEBERRY FILLING

1. 1.Place the blueberries, lemon zest, lemon juice, granulated sugar, and cornstarch in a medium saucepan and stir together.
2. Place the saucepan on the stove over medium heat, stirring frequently until the liquid at the bottom of the pan begins to boil.
3. Reduce the heat and allow the liquid to simmer, stirring constantly, until the liquid becomes thick and jammy (about 3-5 min). It should be able to coat the back of a spoon and the blueberries should still be mostly intact.
4. Remove from the heat and stir in the vanilla extract.
5. Allow the berries to cool for 5 minutes before proceeding.

ASSEMBLE THE BARS

1. Pour the blueberries into the baking pan on top of the base and spread to an even layer.
2. Remove the crumble topping from the refrigerator and sprinkle over the berries. Press the crumble gently into the berries to help it stick.
3. Sprinkle 1 tbsp of rolled oats over the crumble topping.

BAKE THE BARS

1. Bake on the center rack of the oven for 30-35 minutes or until the topping is lightly golden and the berries are bubbling a little around the edges.
2. Allow the bars to fully cool in the pan (~1.5-2 hours).
3. Carefully remove the bars from the pan with the parchment paper, slice, and enjoy!