Prepare a 9x5-inch loaf pan with parchment paper and nonstick cooking spray.
In a large glass bowl, add the chocolate chips, condensed milk and butter. Place in microwave oven, and heat for 10 seconds at a time, stirring after each time, until just melted. Fold in marshmallows and popcorn.
Pour mixture into prepared loaf loaf pan, pressing down to flatten. Dot more popcorn on top. Freeze for 1 hour. Cut into 8 squares. Garnish with powdered sugar before serving.