01 - Preheat the oven to 350°F. Line a 12-cup muffin tin with paper liners.
02 - In a large mixing bowl, whisk together the all-purpose flour, unsweetened cocoa powder, granulated sugar, baking powder, baking soda, and salt until evenly combined.
03 - In a separate medium bowl, whisk the eggs, whole milk, vegetable oil, peppermint extract, and vanilla extract until thoroughly blended.
04 - Pour the wet mixture over the dry ingredients and gently stir until just combined; avoid overmixing to maintain tender muffins.
05 - Fold in semi-sweet chocolate chips, mini marshmallows, and crushed peppermint candies until evenly distributed in the batter.
06 - Divide the batter evenly among the muffin liners, filling each about three-quarters full. Sprinkle extra chocolate chips, mini marshmallows, and additional peppermint candies on top for garnish.
07 - Bake for 18 to 20 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs.
08 - Allow muffins to cool in the pan for 5 minutes, then transfer to a wire rack to cool completely before serving.