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