Preheat and prep: Heat the oven to 350°F (175°C). Line a baking sheet with parchment paper.

Combine dry ingredients: In a medium bowl, whisk almond flour, coconut flour, baking powder, and salt. Break up any lumps for a fine, even texture.

Cream butter and sweetener: In a large bowl, beat the softened butter with the granulated keto sweetener until light and slightly fluffy, about 2 minutes.

Add wet ingredients: Mix in the egg, vanilla, lemon zest, and lemon juice. The mixture may look slightly curdled from the citrus—this is normal.

Bring it together: Add the dry ingredients to the wet and mix until a soft dough forms. Let it rest for 2–3 minutes so the coconut flour hydrates and the dough firms up.

Portion: Scoop about 1 1/2 tablespoons per cookie. Roll into balls and place them on the baking sheet, spacing about 2 inches apart. Gently flatten the tops with your fingers for an even bake.

Bake: Bake for 10–12 minutes, until the edges are just turning golden. The centers should look set but still soft.

Cool: Let the cookies cool on the tray for 10 minutes before moving to a wire rack. They firm up as they cool, so don’t rush this step.

Optional glaze: Whisk powdered keto sweetener with lemon juice until smooth and drizzle over cooled cookies. Allow the glaze to set for 10–15 minutes.