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

Combine dry ingredients: In a large bowl, whisk 2 cups almond flour, 2 tablespoons coconut flour, 1½ teaspoons baking powder, and ¼ teaspoon sea salt. If using, whisk in a pinch (about 1/8 teaspoon) of xanthan gum for extra structure.

Mix wet ingredients: In a separate bowl, whisk 3 large eggs, ½ cup granulated keto sweetener, 5 tablespoons melted butter (cooled) or coconut oil, ¼ cup unsweetened almond milk, 1 teaspoon vanilla extract, 1 tablespoon lemon zest, and 2 tablespoons fresh lemon juice.

Bring it together: Pour the wet mixture into the dry. Stir until just combined. The batter should be thick but spreadable. If it looks dry, add 1–2 more tablespoons almond milk.

Fold in blueberries: Gently fold in 1 cup blueberries. If using frozen, do not thaw; toss them in 1 teaspoon almond flour first to reduce bleeding.

Spread and smooth: Transfer the batter to the prepared pan and smooth the top with a spatula. Scatter a few extra blueberries on top if you like.

Bake: Bake 22–28 minutes, until the top is set, edges are lightly golden, and a toothpick inserted near the center comes out with a few moist crumbs. Avoid overbaking to keep them tender.

Cool completely: Let the bars cool in the pan for 15 minutes, then lift them out using the parchment. Cool fully on a rack before slicing to prevent crumbling.

Optional finish: Dust lightly with powdered keto sweetener or brush with a thin glaze made from powdered sweetener and lemon juice.

Slice and serve: Cut into 9 or 12 squares. Enjoy chilled or at room temperature.