Toast Marshmallows on a skewer over an open flame.
Add eggs to a blender and blend on medium speed. Gradually add the Toasted Marshmallow Syrup and continue to blend for another minute. With the blender still running, add nutmeg, cinnamon, booze, and dairy. Blend for a few seconds more until well combined.
Immediately chill the eggnog to let the flavors blend.