Preheat oven to 350 F. Line cupcake pan with paper cupcake liners. Pull all wet ingredients out of the refrigerator to bring to room temperature. Chop 24-30 Andes mint chocolates into small pieces. These will be used to top each cupcake. I put one chopped andes mint on each cupcake.
Whisk together flour, cocoa powder, salt, baking powder and baking soda together in a small bowl. Set aside.
In the bowl of KitchenAid stand mixer, fitting with a paddle attachment, beat butter, granulated sugar and light brown sugar on medium high speed until fully combined and light and fluffy. Beat about 3 minutes. Scrape the bowl.
Add in eggs and vanilla extract and beat for another 2 minutes.
Add in vegetable oil. Beat on medium speed until just combined. Scrape the bowl.
Add flour and buttermilk alternating with each other. Starting with ⅓ of the flour, mix on low, add ½ the buttermilk, mix on low, add ⅓ flour, mix, add remaining buttermilk, mix and then the remaining flour. Mix until combine.
Fill cupcake liners about ½-¾ full of batter. I like to use a cookie scoop to control the amount being put in so it is the same for each cupcake.
Top each cupcake with chopped Andes Mint Chocolate. I usually use 1 chopped andes chocolate per cupcake. Swirl around gently with a toothpick to combine. Do not over swirl as this will push the chocolates down the cupcake to the bottom and they will stick.
Bake for 16-18 minutes. Cool and top with Mint Chocolate Buttercream.