Preheat the oven to 350 degrees.  Line a cupcake pan with liners, set aside. 

For the cupcakes - In the bowl of a stand mixer, combine the pumpkin puree, sugar, brown sugar and oil.  Mix well. 

Add in the eggs, milk, baking powder, baking soda, cornstarch, cinnamon, nutmeg, salt and vanilla.  Combine until smooth - stopping to scrape down the sides when needed and mixing again. 

Mix in the flour until smooth.  

Fold the mini chocolate chips into the flour mixture with a wooden spoon. 

Scoop enough batter into each cupcake liner to fill about ⅔ full.  Bake in the preheated oven for about 14-16 minutes or until the edges are slightly browned and a toothpick inserted into the center of a cupcake comes out clean. 

Keep a close eye on the cupcakes while they bake. For moist cupcakes, do not overbake. Insert a toothpick into the center, and if it comes out with a few moist crumbs, they're ready!

Allow to cool completely to room temperature on a cooling rack. 

For the Chocolate Buttercream - In the bowl of a stand mixer, combine the softened butter, half the powdered sugar, cocoa powder and 2 tablespoons of milk.  Mix on low speed until combined.

Add in the remaining powdered sugar.

Mix on low speed for about a minute until combined and then bump up the speed to medium for another minute.  If needed, add in the other tablespoon of milk and mix until smooth.  Scrape down the sides and mix again.  

Transfer the frosting to a piping bag fitted with a large star tip.  Pipe a mound of frosting on each cupcake.