I first had this cake when I was pregnant with my first daughter. All I craved was chocolate! I had this cake at a friend's party and I soon later begged her to email her mom for the recipe. I literally dreamt about this cake until I was able to make it on my own...and therein an addiction was born. This is my all-time favorite cake.
Preheat oven to 350. In a saucepan, combine and bring to a boil the 1/2 cup butter, water, and baking squares.
In a separate bowl, combine the flour, sugar, baking soda, and salt. Add the boiling chocolate mixture and beat with a mixer, slowly at first. Add the 2 eggs and sour cream. Beat with mixer until well blended. Pour into a greased 11 x 17 pan. Bake for 20-25 mins until set.
For frosting: combine the butter, milk, and sugar in a saucepan and bring to a boil. Boil for 1 minute. Add the chocolate chips and mini marshmallows. Stir for several minutes until everything is combined and melted. Whisk at the end to make sure all ingredients are combined and there are no chunks. Cool slightly, letting the frosting thicken (several minutes).