01 - Preheat the oven to 350°F. Line a 12-cup muffin tin with paper liners.
02 - In a large bowl, whisk together all-purpose flour, cocoa powder, granulated sugar, baking powder, baking soda, and salt until uniformly distributed.
03 - In a separate medium bowl, whisk the eggs, whole milk, vegetable oil, peppermint extract, and vanilla extract until the mixture is well blended.
04 - Pour wet ingredients into dry ingredients and fold together gently until just combined. Avoid overmixing to maintain tender texture.
05 - Gently fold in semi-sweet chocolate chips, mini marshmallows, and crushed peppermint candies until evenly dispersed.
06 - Divide batter evenly among muffin cups, filling each approximately three-quarters full.
07 - Sprinkle extra chocolate chips, marshmallows, and peppermint candies on top for garnish. Bake for 18 to 20 minutes or until a toothpick inserted into the center emerges with 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.