Popcorn Balls

4 tbsp unsalted butter (plus more for hands)
1 bag (10oz or 283g) white mini marshmallows
¼ c packed brown sugar
3 quarts popcorn (12 cups)
1 c Smarties, M&Ms, pecans (optional)

Melt butter in a heavy saucepan over medium-low heat then add sugar and marshmallows. Stir until marshmallows are melted. Remove from heat and add popcorn and candies/pecans (if using) and toss until well coated. Butter your hands and shape mixture into 2 ½ inch balls and place on a parchment lined baking sheet. Let cool for 30 minutes (do not refrigerate) then place in airtight containers. Will keep for up to a week.