With a torch, carefully toast the top of each marshmallow. If it catches fire just blow it out and keep moving the torch from side to side until you get the desired amount of toasting.
If you don’t have a torch, place the marshmallows on a parchment lined pan and toast them in the broiler before adding them to the top of the doughnut OR just add mini marshmallows to the graham crackers as sprinkles on top!