In a small bowl, whisk together the flour, sugar, cocoa powder, espresso powder, baking powder, and salt. Set aside.
In a separate large bowl, whisk together the vegetable oil, eggs, milk, vanilla, and peppermint extract.
Gently mix in the dry ingredients until just combined. The batter will be thin.
Pour about ¼ cup of batter into each cupcake liner (they should be about halfway full).
Bake at 350°F for 18-22 minutes or until a cake tester comes out clean.
Remove from pan and let cool on wire rack.
Let the chocolate mint cupcakes cool completely before frosting.
White Chocolate Mint Buttercream
Melt the white chocolate and let cool almost to room temperature. It should be melted but cool to the touch. I prefer to melt the chocolate in the microwave in intervals of 20 seconds, stirring each time.
In a large bowl using a handheld or stand mixer fitted with a paddle attachment, cream the butter and powdered sugar together until smooth.
Set the mixer to low speed and slowly drizzle in the melted white chocolate until it's fully incorporated into the buttercream.
Then add in the peppermint extract and green food coloring, and beat on high speed for 3-4 minutes or until the buttercream is super light and fluffy.
If the frosting in too thick, add in 1-2 teaspoons of milk to thin it out a bit.
Frost the cooled cupcakes and garnish with chocolate shavings, thin mint cookies, and a sprig of fresh mint!
Notes
These cupcakes will last in the fridge for up to 3 days. However, they taste best when served at room temperature! I like to let them sit at room temperature for about an hour before serving. Wait to top with thin mints and fresh mint until right before serving.