Preheat oven to 325 degrees. Line 24 muffin cups with paper liners and set aside.
In a bowl, whisk pumpkin, pumpkin spice, eggs, sour cream, buttermilk, oil, and vanilla together. Add in the yellow cake mix and stir just until combined. Do not over mix.
Fill the lined muffing cups halfway full with batter. Bake at 325 degrees for 12-15 minutes just until centers barely spring back.
Allow to cool in the pan for 1 minute, then place them on a wire rack to cool completely before frosting.
To prepare the frosting - in a bowl, whip butter and cocoa powder until creamy. Add in vanilla, salt, and heavy cream.
Add in powdered sugar one cup at a time and beat in. Pipe frosting on cupcakes and sprinkle with mini chocolate chips. Makes 24 cupcakes.