Preheat your oven to 375°F and line a baking sheet with parchment paper. Set aside. Bring your butter, egg, and all remaining ingredients to room temperature—this is crucial for proper mixing and texture. Room temperature butter will cream better with the sweetener, and a room temperature egg will incorporate more smoothly into the batter, creating a lighter, fluffier dough.

In a medium bowl, whisk together the almond flour, coconut flour, xanthan gum, baking soda, cream of tartar, and kosher salt. Mix thoroughly to ensure the leavening agents and binders are evenly distributed throughout the dry mixture. Set aside. I like to sift this mixture rather than just whisking—it breaks up any clumps in the almond flour and gives you a more tender cookie in the end.

Beat the softened butter in a separate bowl for 1-2 minutes until pale and creamy. Add the erythritol and allulose, then beat the mixture for 8 minutes on medium speed until it becomes light, fluffy, and noticeably increased in volume. This extended creaming incorporates air into the butter, which helps the cookies rise and creates a lighter texture. The sweetener crystals will gradually dissolve and incorporate fully.

Add the vanilla extract and room temperature egg to the creamed butter mixture, beating until fully incorporated and smooth. Then add half of the dry ingredient mixture from Step 2, mix until just combined, then add the remaining dry ingredients and mix until the dough just comes together. Be careful not to overmix after adding the flour—this can toughen the cookies. The dough should be soft and slightly sticky.

In a small shallow bowl, combine the freshly ground cinnamon with 1-2 tablespoons of your remaining erythritol (or use a 1:1 ratio to taste) to create the cinnamon 'sugar' coating. Scoop the dough using a cookie scoop or spoon into small balls, then roll each ball in the cinnamon mixture until well coated on all sides. Gently flatten each cookie slightly with your palm or the bottom of a glass, creating about ¼-inch thick discs. Arrange them on the prepared baking sheet with about 1 inch of space between each cookie.

Bake the cookies in the preheated 375°F oven for 6-8 minutes, until the edges are light golden brown but the centers still look slightly underdone—they will continue to cook on the baking sheet after removal. Let the cookies cool on the baking sheet for 10 minutes to set and firm up before transferring to a wire rack. I find that moving them too early causes them to fall apart, but letting them sit on the warm pan ensures they maintain their shape and develop a slightly crispy exterior while staying tender inside.