Preheat oven to 350 degrees F (175 degrees C). Not necessary to grease pan.
In a sauce pan, combine 1 1/4 cup water and 1/4 cup butter or margarine. Heat until butter melts, then stir in brown sugar and coconut. Pour into ungreased 9×13 inch pan. Sprinkle marshmallows and nuts over top. set aside.
For the cake: in a saucepan over low heat, combine chocolate with 1/2 cup water. Heat, stirring, until chocolate is melted. Remove from heat.
In a large bowl, mix flour, sugar, soda and salt. Add sour cream, 1/2 cup butter or margarine, vanilla and eggs. Add chocolate mixture and beat 3 minutes. Carefully spoon batter over coconut marshmallow mixture in pan.
Bake at 350 degrees F (175 degrees C) for 40 to 50 minutes, or until toothpick inserted into center comes out clean. Place pan on foil or cookie sheet to guard against spillage.
Source: Read Full Article