Truth be told, I had never in my life had a popcorn ball until I was in my mid to late 30's. My husband mentioned in passing that his grandma always made popcorn balls around Halloween. Being the wonderful (and humble) wife that I am, I surprised him with a batch of these ooey-gooey treats one year and it has now become a tradition that the girls and I enjoy working on together.
1/2 stick of butter
1 regular size bag of marshmallows
1/2 tsp. vanilla
1/4 tsp. salt
3 quarts of popped corn
Melt the butter and marshmallows either in the microwave or over low heat on the stove. Once the butter/marshmallows are melted, stir in the salt and vanilla. (You could also add food coloring at this point if you wanted.)
Pour the melted mixture over the popcorn and stir well, making sure you get all of the popcorn covered. Let the popcorn mixture cool slightly to avoid getting burnt. Next, butter your hands....yes, really, and the kids will love it, trust me. Use your buttered hands to shape the popcorn into the desired size, pressingly tightly to make the "ball" stick together.
Have a non buttered person (snicker) ready with the plastic wrap, so that the process will move quickly. You'll want to wrap the popcorn balls pretty tightly to keep them from getting stale. Cleanup can be a bit sticky (har har har). Let your items soak in hot water for a few moments and you'll be good to go.
You could add food coloring or cinnamon candy flavoring to add a bit of fun to your creations. You could also add peanuts, M&M's or other candy to the popped corn before add the marshmallow mixture.