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

Cream the butter and sweetener: In a mixing bowl, beat 1/2 cup softened unsalted butter with 1/2 cup granulated erythritol (or allulose) until light and slightly fluffy, about 2–3 minutes.

Add egg and flavors: Beat in 1 large egg, 1 teaspoon vanilla extract, 1–2 teaspoons lemon zest, and 1 tablespoon fresh lemon juice. Mix until smooth. The batter may look slightly curdled at first; it will come together once dry ingredients are added.

Combine dry ingredients: In another bowl, whisk 1 3/4 cups finely blanched almond flour, 1 tablespoon coconut flour, 1/2 teaspoon baking powder, and 1/4 teaspoon fine sea salt.

Make the dough: Add the dry mixture to the wet ingredients. Mix on low until a soft dough forms. If the dough seems sticky, let it rest for 5 minutes so the coconut flour absorbs moisture.

Portion: Scoop 1 to 1 1/2 tablespoon portions and roll into balls. Place 2 inches apart on the baking sheet. Gently flatten to about 1/2 inch thick with your fingertips or the bottom of a glass.

Bake: Bake 10–12 minutes, until the edges are just turning golden. The centers will still look soft; that’s okay.

Cool: Let cookies cool on the tray for 10 minutes to set, then transfer to a rack to cool completely. They firm up as they cool.

Optional lemon glaze: Stir 1/2 cup powdered erythritol with 1–2 tablespoons lemon juice until smooth. Drizzle over cooled cookies. Let the glaze set before serving.