01 - Preheat oven to 350°F (175°C). Line two baking sheets with parchment paper.
02 - In a medium bowl, whisk together almond flour, coconut flour, erythritol, baking powder, and salt.
03 - In a large bowl, beat softened butter until creamy. Add egg, peppermint extract, and vanilla extract; mix until smooth.
04 - Gradually stir dry ingredients into the wet mixture until a dough forms.
05 - Divide dough in half. Add a few drops of red food coloring to one half and knead until color is marbled (do not overmix for best swirl effect).
06 - Take small pieces from each dough half and gently twist together to form 1-inch balls, then slightly flatten onto prepared baking sheets, spacing 2 inches apart.
07 - If desired, sprinkle cookies with crushed sugar-free peppermint candies.
08 - Bake for 10-12 minutes, or until edges are just golden. Let cool on the pan for 5 minutes, then transfer to a wire rack to cool completely.