Monster Brownies

Ingredients:

• 1 pan (9 by 13 in.) brownies, chilled at least 2 hours
• 6 milk or dark chocolate bars (or a combination), such as Guittard or Hershey's, each about 1/4 in. thick and 1.5 oz. to 2.6 oz., broken into 2- to 2 1/2-in. squares
• 1/2 cup mini marshmallows
• 2 cups regular marshmallows
• 1 to 2 tbsp. regular M&M's
• 1 to 2 tbsp. mini M&M's