01 - Preheat oven to 350°F. Line a 12-cup muffin tin with paper liners.
02 - In a large bowl, whisk together flour, cocoa powder, sugar, baking powder, baking soda, and salt until uniform.
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 gently stir until just combined. Avoid overmixing to ensure a tender crumb.
05 - Fold in chocolate chips, mini marshmallows if using, and crushed peppermint candies.
06 - Divide batter evenly among muffin cups, filling each about three-fourths full.
07 - Top each portion with extra chocolate chips, marshmallows, and additional crushed peppermint candies as desired.
08 - Bake for 18 to 20 minutes, or 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.