Preheat the oven to 350°F.
Line a baking sheet with parchment paper or a silicone baking mat.
In a medium bowl, whisk together the almond flour, coconut flour, baking powder, salt, and optional xanthan gum.
In a large bowl, beat the softened butter and keto sweetener for two to three minutes, until lighter and slightly fluffy.
Beat in the egg, vanilla extract, and optional butter extract.
Gradually add the dry ingredients and mix just until a soft dough forms.
Fold in the sugar-free chocolate chips.
Refrigerate the dough for 15 to 20 minutes if it feels very soft.
Scoop the dough into approximately 18 portions and arrange them two inches apart on the baking sheet.
Gently flatten each cookie.
Bake for 10 to 13 minutes, until the edges are lightly golden and the centers still look slightly soft.
Let the cookies cool on the baking sheet for 10 minutes.
Transfer them carefully to a cooling rack.
Sprinkle with optional flaky sea salt and allow them to cool completely.