Preheat oven to 350°F and line a cupcake pan with 12 liners.

In a bowl, whisk together flour, cocoa powder, baking powder, baking soda, salt, and granulated sugar.

In another bowl, whisk together eggs, milk, vegetable oil, and vanilla extract.

Gradually add wet ingredients to dry ingredients. Stir in the boiling water slowly.

Divide the batter into cupcake liners, filling each about 2/3 full.

Bake for 18-20 minutes or until a toothpick comes out clean.

Let cupcakes cool for 5 minutes in the pan, then transfer to a wire rack to cool completely.

Use a knife or corer to remove centers from cooled cupcakes.

Insert 3 mini marshmallows into each cupcake center and replace the tops.

Heat heavy cream until simmering, then pour over the chocolate chips in a bowl.

Let sit for 5 minutes, then stir until smooth. Chill for 30 minutes.

Whip the ganache until fluffy, then frost the cupcakes.

Top with extra marshmallows or crushed peppermint if desired.