01 - Preheat oven to 350°F. Line a baking sheet with parchment paper.
02 - In a large bowl, beat softened butter and erythritol together until light and fluffy, approximately 2 minutes.
03 - Beat in the egg and vanilla extract until fully incorporated.
04 - In a separate bowl, whisk together almond flour, coconut flour, baking soda, cream of tartar, and salt until well blended.
05 - Gradually add dry ingredients to wet mixture, mixing until a soft, pliable dough forms.
06 - Scoop tablespoon portions of dough and roll into balls. Place 2 inches apart on prepared baking sheet and flatten gently with palm or glass bottom.
07 - Bake for 10 to 12 minutes until edges are lightly golden. Avoid overbaking to maintain soft texture.
08 - While cookies bake, combine erythritol and cinnamon in small bowl for topping mixture.
09 - Remove cookies from oven and cool 5 minutes on pan. Brush lightly with melted butter, then sprinkle generously with cinnamon mixture. Cool completely on wire rack before serving.