In the large bowl of an electric mixer combine flour, sugar, cinnamon, baking powder, baking soda, xanthan gum, salt and nutmeg. Whisk the dry mixture until evenly combined.
With electric mixer on low add the sour cream (first amount) and butter. Beat for 2 minutes.
In another bowl combine eggs, sour cream (second amount) and vanilla. Add half the mixture to the large bowl and beat until mixed in. Add the remainder of the mixture then increase speed to medium-high and beat until light and fluffy, about 2 minutes.
Using mini or regular size muffin tins; grease or line with silicone or paper muffin liners. Using a portion scoop fill muffin tins ½ - ¾ full.
Bake in 350°F oven 18 minutes for mini muffins or 20 minutes for regular size muffins.
Cool on rack 5 minutes before carefully removing each muffin from the pan. Cool completely on wire racks before adding cinnamon-sugar topping.