Warm the water, butter, and granulated sweetener in a pot until the mixture reaches a full boil. Look for melted butter and active bubbling across the surface.

Remove the pot from the heat, then stir in the almond flour, coconut flour, xanthan gum, and salt until a thick dough forms. The dough should pull away from the sides of the pot and gather into a smooth, resistant mass.

Transfer the dough to a bowl and allow the heat to settle slightly before mixing in the egg. Keep mixing until no streaks of egg remain and the dough forms one cohesive, pipeable ball.

Fill a churro maker with the dough, pressing out any trapped air as you load it. The dough should emerge in defined ridges rather than breaking into crumbs.

Heat the oil in a large skillet before adding the dough. The surface should shimmer and give a steady sizzle when dough reaches it.

Pipe lengths of dough into the hot oil and cook for 1-2 minutes, then turn and cook for another 1-2 minutes. Take them out when the ridges are golden amber and the sizzling has calmed slightly.

Lift the churros from the skillet and set them on paper towels to remove excess oil. They should feel firm on the outside while still warm and tender within.

Roll the warm churros in the granulated sugar substitute and cinnamon. Coat every ridge while the surface is warm so the crystals adhere evenly.