Preheat oven to 350. Grease 6 cup bundt pan with oil or cooking spray.
Whisk together the sour cream, egg, vanilla, oil, butter & sugar in a bowl.
Add flour, soda, salt, & nutmeg (optional) & stir together until well combined.
Fill pan with batter & bake for 20-23 minutes or until the top is springy to the touch & the sides are turning golden brown. Remove from oven & let cool in pan for 5-10 minutes then transfer to cooling rack. Make the cinnamon & sugar topping.
For the cinnamon & sugar coating: Melt 2 Tablespoons of butter in microwave. Mix cinnamon & sugars together in a bowl. Brush the cake top and sides with butter, sprinkle with cinnamon & sugar mix.
Recipe by THE SEMISWEET SISTERS at https://www.thesemisweetsisters.com/2018/08/22/cinnamon-churro-donut-bundt-cake/