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

Make the cherry filling: In a small saucepan, add 2 1/2 cups pitted tart cherries (frozen is fine), 1/3 cup sweetener, 1 tablespoon lemon juice, and a pinch of salt. Cook over medium heat, stirring, until cherries release juices and simmer, about 5–7 minutes.

Thicken the filling: Stir in 1–2 teaspoons chia seeds and simmer 1–2 minutes more until slightly thickened. Taste and adjust sweetness. Remove from heat and let it cool to thicken further. Add 1/2 teaspoon vanilla and a drop of almond extract if using.

Mix the crust/crumb: In a bowl, whisk 2 cups almond flour, 2 tablespoons coconut flour, 1/3–1/2 cup powdered sweetener, 1/4 teaspoon salt, and a small pinch of xanthan gum (optional). Melt 1/2 cup (1 stick) butter and let it cool slightly. Stir in 1 beaten egg and 1 teaspoon vanilla, then pour into the dry mixture. Mix until a soft, crumbly dough forms.

Form the crust: Set aside about 3/4 to 1 cup of the dough for the crumble topping. Press the remaining dough firmly and evenly into the lined pan to form the base.

Par-bake: Bake the crust for 10–12 minutes, until the edges look slightly set but not browned. Remove from the oven.

Layer it up: Spread the cooled cherry mixture evenly over the warm crust. Sprinkle the reserved dough over the top, pinching small clumps to create a crumb topping.

Bake: Return to the oven and bake 18–22 minutes, until the top is lightly golden and the cherries are bubbling at the edges.

Cool completely: Let the pan cool on a rack for at least 1 hour, then refrigerate 1–2 hours for the cleanest slices. Lift out using the parchment and cut into bars.

Serve: Enjoy as is, or add a spoonful of lightly sweetened keto whipped cream. A sprinkle of lemon zest on top is nice too.