Preheat oven to 350F, spray a donut tray with cooking spray.

In a saucepan over medium heat, melt the chocolate with the buttermilk.

In a bowl, cream the butter, egg, and sugar together.

Incorporate the melted chocolate, flour, yeast, and vanilla.

Stir constantly until uniform.

Fill the donut pan with batter.

Bake for 15 minutes or until done.

Remove pan from the oven, and let cool.

Prepare sugar glaze by whisking together powdered sugar, milk, and vanilla. Dip ½ of each donut in glaze and top with grated chocolate and marshmallows.

Serve and enjoy.