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