Preheat the oven to 350F degrees. Line cupcake pan with cupcake liners. Set aside.
In a large bowl using an electric mixer, mix together boxed cake mix, milk, butter, eggs, vanilla, and cinnamon on low speed for 1 minute. Scrape down sides of bowl; beat on medium speed for 2 minutes.
Scoop batter into cupcake liners, no more than ⅔ full. Bake for about 12-15 minutes. Insert a toothpick into the center of the cupcake, if it comes out clean it is done. Remove cupcakes from oven and allow cupcakes to cool in cupcake pan for 5 minutes; transfer to wire rack and cool completely. Cupcakes should be cooled completely before frosting.
For Cinnamon Buttercream
In a large bowl using an electric mixer, cream butter and shortening until creamy and smooth. Add salt and water; mix until combined.
Turn mixer on lowest speed and slowly add 1 lb of powdered sugar; mix until creamy. Scrape down bowl as necessary.
Turn mixer on medium speed for 1 minute. Turn mixer to slowest speed. Slowly add remaining 2 lbs powdered sugar and clear vanilla extract. Blend until creamy.
Add ground cinnamon to buttercream; mix on high speed for 4 minutes, or until fluffy.
Frost using a decorating tip or spatula onto cooled cupcakes. Eat & Enjoy!
Store Snickerdoodle Cupcakes in an airtight container. Cupcakes will keep for 4 days.Store Cinnamon Buttercream in an airtight container in a cool non-refrigerated environment for up to 2 weeks, or refrigerate for 1-2 months. When you are ready to use, re-whip it.
Snickerdoodle Cupcakes with Cinnamon Buttercream | https://sarahsbakestudio.com/snickerdoodle-cupcakes/