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, cocoa powder, granulated sugar, baking powder, baking soda, and salt.
03 - In a separate bowl, whisk eggs, whole milk, vegetable oil, peppermint extract, and vanilla extract until fully blended.
04 - Pour wet ingredients into dry ingredients and mix gently until just combined. Avoid overmixing to maintain a tender crumb.
05 - Gently fold in semi-sweet chocolate chips, mini marshmallows if using, and crushed peppermint candies until evenly distributed.
06 - Divide batter evenly among prepared muffin cups, filling each about three-quarters full.
07 - Sprinkle extra chocolate chips, mini marshmallows, and additional crushed peppermint candies over the batter for garnish.
08 - Bake for 18 to 20 minutes until a toothpick inserted in the center emerges with a few moist crumbs.
09 - Allow muffins to cool in the pan for 5 minutes, then transfer to a wire rack to cool completely before serving.