Cupcakes:
4 ounces milk or semisweet chocolate, chopped
⅓ cup cocoa powder
¾ cup hot coffee or water
6 tablespoons canola oil
2 large eggs
2 teaspoons white vinegar
1 teaspoon vanilla extract
¾ cup all-purpose flour
½ cup granulated sugar
¼ cup brown sugar
½ teaspoon salt
½ teaspoon baking soda

Marshmallow Filling:
1 large egg white
¼ cup granulated sugar
⅛ teaspoon cream of tartar
½ teaspoon vanilla extract

Nutella Frosting:
½ cup butter, room temperature
¼ cup Nutella or other chocolate hazelnut spread
3 cups powdered icing sugar
1 tablespoon heavy cream or milk

Garnish:
marshmallow bits
crumbled graham crackers