You can find the complete recipe in Martha Stewart Site.
This is my husband favorite brownie recipe and to welcome him after a two week trip. I baked it today again!
Melting the butter and chocolate
Few tips: After you sprinkle the toppings, don't bake it for 5 more minutes as the recipe says. I usually turn off the oven and leave it for couple minutes just to warm the marshmallows and promptly I take it out. If the chocolate chips and marshmallows melt completely it will get very messy. Be sure it is cool before you cut, I usually don't follow this step because I can't resist the wait. I love it warm.
This is a warm piece melting, very rich, very tasty, very delicious.