Preheat oven to 350°F. Place cupcake liners into muffin cups.
Place cake mix in the bowl of an electric stand mixer. Add pudding, buttermilk, oil, and eggs. Mix to combine well.
Fill cupcake liners 2/3 full and bake for 15-17 minutes. Remove from oven and set cupcakes on cooling rack to cool.
Prepare frosting by blending butter with an electric hand mixer until smooth. Add 2 Tbsp milk, vanilla extract, and cocoa. Mix well.
Add powdered sugar ½ c. at a time. Add remaining milk and blend well.
Frost cooled cupcakes and top with miniature chocolate chips.