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