Preheat oven to 350F degrees. Line (1) cupcake pan with 12 cupcake liners. Set aside.
In a medium bowl, mix flour, unsweetened cocoa powder, baking powder, baking soda and salt. Set aside.
In a large bowl, using an electric or stand mixer on medium speed, beat eggs and sugar for about 2 minutes, or until light and creamy.
Add the butter and vanilla extract and beat on low speed for about 1 minute, or until well blended.
Beat in the dry ingredients on low speed until blended. DO NOT OVER MIX!
Add the sour cream and beat until smooth.
Fill each cupcake liner about 3/4 the way full with cupcake batter. Bake 18 to 20 minutes or until toothpick inserted in center comes out clean. Allow cupcakes to cool before frosting.
MAKE CARAMEL BUTTERCREAM FROSTING:
Using an electric or stand mixer, cream together butter, corn syrup, and vanilla extract until light and fluffy. Beat for about 3 minutes.
Slowly, add powdered sugar and heavy whipping cream. Mix until frosting becomes light and fluffy, adding milk until the mixture reaches desired consistency. Add caramel sauce and mix until combined.
Frost cooled cupcakes using a piping bag or knife. Top with SPRINKLES & a Twix bar.
Notes
For the frosting, heavy cream or half-and-half will give your frosting the creamiest texture. You may use milk instead, but the frosting won't be as creamy.