Preheat oven to 325 degrees. Line bottom and sides of a 9×11 square glass baking pan with parchment paper; butter the heavy-duty parchment paper. Set aside.
Place butter and chocolate in a large 2-quart double boiler; stir frequently, until almost melted. Remove from heat; stir until completely melted. Whisk in sugar and salt until smooth; whisk in eggs. Gently whisk in flour just until you reach a smooth texture.
Spread batter evenly in prepared 9 x 11 glass baking pan. Using a tablespoon, drizzle 1/4 of a cup of caramel sauce in 4 long vertical lines down the top of brownie batter. Using a butter knife make a slicing motion 5 times across the brownie mixture.
Place in 325-degree oven – bake until a toothpick inserted in center comes out clean about 50-55 minutes. Cool completely in pan.
Use heavy-duty parchment paper to lift brownie cake from pan; peel off the paper and discard. Cut into desired size squares.
Place cut brownies on a metal baking sheet, top cooled brownies with several small marshmallows, place in refrigerator for 45 minutes.
After 45 minutes, remove brownies and drizzle warm not hot Mock Caramel Sauce over brownies ( refrigerate brownies once done for about 20 minutes before serving.)