Preheat the oven to 350F degrees and line 2 12-cavity muffin tins with cupcake liners. The recipe will make about 18-20 cupcakes total.
First - whisk together the dry ingredients (flour, cocoa, baking soda, baking powder and salt) in a large bowl.
In a separate large bowl beat together the oil, sugar, eggs, vanilla and sour cream using a stand or hand-held electric mixer until combined and no sugar lumps remain. With the mixer on low speed add in about half of the flour mixture followed by half of the buttermilk until combined. Turn off the mixer and scrape down the sides of the bowl as needed. Repeat with the second half of the flour mixture and buttermilk until smooth.
Spoon the batter into the prepared muffin pan - you should end up with 18-20 cupcakes total. Bake for 15-17 minutes until an inserted toothpick comes out clean. Allow to cool fully before frosting.
While the cupcakes are cooling, make the frosting. Using a stand or hand-held electric mixer beat the butter on medium speed until the color has lighted and the butter is fluffy. Turn down the mixer to low and add in about 1/2 to 1 cup of icing sugar at a time. After almost combined, turn the mixer to high speed and beat for 5-10 seconds. Repeat with the rest of the icing sugar. Once almost all of the icing sugar has been added, beat in the whipping cream 1 tablespoon at a time until the desired consistency is reached. Then add in the mint extract about 1/2 teaspoon at a time along with the green food coloring until the desired color and level of minty-ness is reached.
Frost the cupcakes using a piping bag or with the flat-edge of a knife. Sprinkle with mini chocolate chips for decoration.