Microwave 1 cup butter and semisweet chocolate in a large microwave-safe glass bowl at HIGH 1 minute or until melted and smooth, stirring every 30 seconds.
Whisk sugar and next 5 ingredients into chocolate mixture. Pour batter into a greased 15- x 10- x 1-inch jelly-roll pan.
Bake at 350° for 20 minutes. Remove from oven, and sprinkle evenly with miniature marshmallows; bake 8 to 10 more minutes or until golden brown. Microwave 1/2 cup bottled caramel sauce at HIGH 15 seconds. Drizzle over browned marshmallows. Drizzle with Chocolate Frosting, and sprinkle with 1 cup dry-roasted peanuts.