Preheat the oven: Set to 350°F (175°C). Line a baking sheet with parchment paper.
Mix dry ingredients: In a medium bowl, whisk almond flour, coconut flour, baking soda, salt, and xanthan gum if using.
Break up any clumps.
Cream butter and sweetener: In a large bowl, beat softened butter with the keto sweetener until light and creamy, 2–3 minutes. This helps the cookies spread and brown.
Add egg and vanilla: Beat in the egg and vanilla until smooth. Scrape the bowl so everything mixes evenly.
Combine: Add the dry ingredients to the wet.
Mix until a thick dough forms. It should be soft but not sticky.
Fold in chocolate: Stir in sugar-free chocolate chips and nuts if using.
Portion: Scoop 1 1/2-tablespoon mounds onto the baking sheet, spacing about 2 inches apart. Gently flatten the tops with your fingers for even baking.
Bake: Bake 9–12 minutes, until the edges are set and lightly golden.
The centers will look slightly soft—that’s good.
Cool: Let cookies cool on the sheet for 10 minutes, then transfer to a rack. They firm up as they cool.
Serve: Enjoy warm, or let them cool fully for the best chewy texture.