Preheat your oven to 350°F and line a muffin tin with 9 muffin liners inside. Set it aside.
In a medium size mixing bowl sift all-purpose flour, baking powder, baking soda, and salt together. Set aside.
In another large mixing bowl cream together softened butter and granulated sugar (you can use a mixer or a whisk). Add eggs, sour cream, milk, and vanilla extract, whisking constantly in between.
Add dry ingredients into the mixture. Using a spatula, fold it together until smooth. Do not over mix.
Add chocolate chips to the mixture and fold it together.
Divide this batter between 9 muffin liners. Bake at 350°F for 18-20 minutes or until a toothpick comes out clean. When it is ready, take it out and set aside to cool off for about 10 minutes. Place the muffins on a wire rack.
For the frosting, using a hand or stand mixer, cream together softened butter and powdered sugar on high speed for 3-5 minutes. Add cocoa powder and mix it until combined. Add heavy cream and beat it until everything is well incorporated and has stiff peaks.
When the cupcakes are completely cooled off, top them with the Chocolate Frosting using a large star piping tip.