In a bowl, whisk almond flour, coconut flour, and salt. In a separate large bowl, beat the softened butter and Swerve until creamy. Add egg and vanilla, then beat in the flour mixture until a dough forms.
Lightly dust a work surface with coconut flour. Pat the dough into a circle, place a piece of parchment on top, and roll to 1/3‑inch thickness. Use Halloween-shaped cookie cutters to cut out cookies. Place on parchment‑lined baking sheets and freeze for 30 minutes.
Preheat oven to 325°F. Bake frozen cookies for 12–14 minutes, rotating pans halfway, until edges just start to brown. Let cool completely on the sheets (cookies will firm up as they cool).
Whisk together both powdered sweeteners and egg white powder. Add water 1 tablespoon at a time until the icing drizzles in ribbons. Stir in vanilla. Divide and tint with natural food coloring.
Pipe outlines on cooled cookies, let dry 10–20 minutes, then “flood” inside the outlines with more icing. Use a toothpick to spread evenly. Let dry completely before stacking.
Notes
Nutrition per serving: Calories: 177 | Total Carbs: 4.8g | Net Carbs: 2.4g | Fats: 15.2g | Protein: 5g