Preheat the oven to 350 degrees. Line the muffin pan with paper baking cups.

Place the cake mix, milk, melted butter, eggs, vanilla, and cinnamon in a large mixing bowl. Blend with an electric mixer on low speed for 1 minute. Stop the machine and scrape down the sides of the bowl with a rubber spatula. Increase the mixer speed to medium and beat 2 minutes more, scraping the sides down again if needed. The batter should look well combined.

Divide the batter into the paper baking cups in the cupcake pan. Place in the oven.

Bake for 15-20 minutes. Check doneness by inserting a wooden toothpick into the center of the cupcake. If the toothpick comes out clean, the cupcakes are done.

Allow to cool for 5 minutes before decorating to taste.