Place marshmallows on a piece of parchment paper on an 8x12 cookie sheet. Broil in oven until tops are well toasted (almost burnt, but not quite). Rotate and repeat until all side of the mashmallows are toasted.
In a bowl whisk together sugar, milk powder, and xanthan gum.
In a pot add milk and corn syrup.
Whisk dry ingredients into the pot of liquid ingredients. Be sure to mix well.
Add toasted marshmallows and heat ingredients for ~5 minutes on medium heat, stirring well, until sugar is disolved.
Add remaining cream and allow mixture to cool for a few minutes.
Blend mixture in a blender, then place in a sealed contained. Refridgerate for 12+ hours.
Churn according to your ice cream maker's instructions.
About 5 minutes before churning is complete, add graham cracker chunks and ganache bits.
Layer about 1/2 of the ice cream into a container, then top with chocolate syrup, and layer the remaining ice cream on top. Freeze for 4+ hours before serving.