In a large bowl or bowl of a stand mixer, beat together the cake mix, oil, buttermilk, eggs, and cinnamon on medium speed for 2-3 minutes.
Scoop the cupcake batter into the muffin tins, filling 2/3 of the way full.
Bake for 15 minutes, then remove from the oven and transfer to a wire rack.
While the cupcakes are still warm, dip the tops in a small bowl of cinnamon sugar, then allow them to finish cooling.
Cream butter, cream cheese, vanilla, and cinnamon in a medium bowl.
Beat the powdered sugar into the cinnamon buttercream. Add a tablespoon of milk or cream at a time. Continue mixing until the icing is thick but pipeable.
Transfer the frosting to a piping bag and decorate.
Drizzle with caramel sauce and add a churro to the top of the frosting.