Prep the pan and oven: Preheat oven to 350°F (175°C). Line an 8x8-inch baking pan with parchment, leaving overhang for easy lifting. Lightly grease the sides.

Make the crust: In a bowl, mix 2 cups almond flour, 2 tablespoons coconut flour, 1/3 to 1/2 cup granulated keto sweetener, and a pinch of salt. Add 1/2 cup melted unsalted butter and 1 teaspoon vanilla. Stir until it forms a soft, sandy dough.

Par-bake the crust: Press the dough firmly and evenly into the pan. Bake for 10–12 minutes, until set and just starting to turn golden at the edges. Set aside.

Make the blueberry layer: In a saucepan, add 2 1/2 cups blueberries, 2–3 tablespoons granulated sweetener, 1 tablespoon lemon juice, zest of half a lemon, and a pinch of cinnamon. Cook over medium heat for 5–7 minutes, stirring, until the berries release juices and start to thicken.

Thicken the filling (optional but helpful): Sprinkle in 1/4 teaspoon xanthan gum while whisking, or stir in 1 tablespoon chia seeds. Cook 1–2 more minutes until jammy. Remove from heat to cool slightly.

Make the crumble topping: In a bowl, combine 3/4 cup almond flour, 1 tablespoon coconut flour, 2–3 tablespoons powdered or granulated sweetener, a pinch of salt, and 2 tablespoons cold butter cut into small pieces. Use your fingers to rub into coarse crumbs. For extra crunch, add 2 tablespoons unsweetened shredded coconut or chopped nuts.

Assemble: Spread the blueberry mixture over the warm crust. Sprinkle the crumble evenly over the top.

Bake: Return the pan to the oven for 18–22 minutes, until the topping is lightly golden and the blueberry filling is bubbling at the edges.

Cool completely: Let the bars cool in the pan, then chill for at least 1 hour to set. This helps them slice cleanly.

Slice and serve: Lift using the parchment, cut into 9–12 bars, and enjoy. Optional: dust with a bit of powdered keto sweetener or serve with whipped cream.