01 - Preheat the oven to 350°F. Line a 12-cup muffin tin with paper liners.
02 - In a large bowl, whisk together the all-purpose flour, unsweetened cocoa powder, granulated sugar, baking powder, baking soda, and salt until fully incorporated.
03 - In a separate bowl, whisk the eggs, whole milk, vegetable oil, peppermint extract, and vanilla extract until smooth and well blended.
04 - Pour the wet mixture into the bowl with the dry ingredients and stir gently until just combined. Avoid overmixing to ensure tenderness.
05 - Fold in the semi-sweet chocolate chips, mini marshmallows, and crushed peppermint candies, distributing evenly throughout the batter.
06 - Divide the batter evenly among the muffin cups, filling each about three-quarters full. Sprinkle extra chocolate chips, marshmallows, and peppermint candies on top for garnish.
07 - Bake for 18 to 20 minutes, or until a toothpick inserted into the center of a muffin emerges with a few moist crumbs but no wet batter.
08 - Allow muffins to cool in the pan for 5 minutes before transferring to a wire rack to cool completely.