01 - Preheat oven to 350°F. Line a 12-cup muffin tin with paper liners.
02 - In a large mixing bowl, whisk together flour, cocoa powder, granulated sugar, baking powder, baking soda, and salt until evenly blended.
03 - In a separate bowl, whisk eggs, whole milk, vegetable oil, peppermint extract, and vanilla extract until smooth and well combined.
04 - Pour wet mixture over the dry ingredients and gently mix just until incorporated. Avoid overmixing to preserve a tender crumb.
05 - Gently fold chocolate chips, mini marshmallows, and crushed peppermint candies into the batter.
06 - Divide batter evenly among the muffin cups, filling each about three-quarters full.
07 - Sprinkle each portion with extra chocolate chips, mini marshmallows, and additional crushed peppermint candies as desired.
08 - Bake on the center rack for 18 to 20 minutes, or until a toothpick inserted into the center comes out with moist crumbs attached.
09 - Allow muffins to cool in the pan for 5 minutes. Transfer to a wire rack to cool completely before serving.