Preheat oven to 350 degrees and spray your donut pan with cooking spray.
In a large bowl whisk together the flour, nutmeg, baking soda and salt. Set aside.
In a separate medium bowl, whisk together melted butter, sugars, egg and vanilla. Once no sugar lumps are left, whisk in sour cream and coconut milk. Pour wet ingredients into dry and whisk until combined.
Spoon the batter into a large ziploc bag, seal and cut off one corner. Pipe the donut batter into your donut pan cavities and fill ½ full.
Bake for 5 - 7 minutes or until you gently touch the top of your donuts and it springs back and feels slightly firm.
Remove from oven, cool for 5 minutes and move to cooling rack.
When donuts are cool, in a small bowl stir together sugar and cinnamon for the topping.
Brush both sides of each donut, one at a time, then roll each donut in cinnamon sugar and place on your wire cooling rack.