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