In a blender mix 1 cup milk with the egg nog, sugar, eggs and vanilla. Blend on medium speed for 3-5 minutes. Pour the rest of the gallon of milk into a punch bowl or super large bowl. Mix in the blender mix. It will stir or mix itself. Top with vanilla ice cream the entire 1/2 gallon. Easier if ice cream is softer. Sprinkle with nutmeg. Let sit for about 3 minutes for flavors to blend. Serve and enjoy. Better with ice cream in each cup. This recipe can be used with out store bought egg nog for those who desire the taste to not be as strong.