Pop enough popcorn to make at least a gallon. Place in a large bowl and set aside. Microwave popcorn works great. I like to get the kind that is just plain.
In a microwavable bowl melt 1/2 cup butter, add 4 cups miniature marshmallows and cook a few seconds at a time stirring after each time you check them. Once they are all melted pour over popcorn, mix and make into balls.
If you want to make them a little different add a few m&ms or nuts, red cinnamon candies are nice too. I like to get colored plastic wrap to wrap them. You may also add a little food coloring to make them Christmas colors. Add just a few drops at a time to your mixture until you get the color you want.