Preheat the oven to 350F degrees and adjust the oven rack to the middle position. Liberally grease the wells of a 6 cup donut pan.
In a small mixing bowl, whisk together the almond flour, arrowroot flour, coconut flour, tapioca flour, baking powder, and salt.
In a medium mixing bowl add the egg, milk, maple syrup, melted oil, and vanilla extract. Whisk until thouroughly combined. Sprinkle the dry ingerdients over the wet ingredients and mix until no dry streaks remain.
Pour, scoop, or spoon the batter equally into the prepared donut pan. Bake the donuts for 18 to 22 minutes, or until they are springy to the touch and a light golden brown.
Cool the donuts in the pan set on a wire cooling rack for 5 minutes. Then invert the pan to relase the donuts, and let the donuts cool completely on the wire rack. If any stick, gently run a knife or offset spatula around the donuts to release them from the pan.