Chocolate Lover's Chocolate Pudding Cake

1 chocolate cake mix - prepared-not baked!
2 c. warm water
1 c. brown sugar
1/2 c. cocoa
1/2 pkg. miniature marshmallows
1 c. chopped walnuts
Top with Cool Whip

Mix water, sugar and cocoa.  Pour water mixture into greased 9X13 cake pan.  Sprinkle marshmallows over water mixture.  Spoon cake batter carefully over marshmallows. Sprinkle walnuts over all.  Bake according to directions on cake box. Top with dollop of Cool Whip when serving.
 
If cake pan seems too full when spooning batter over marshmallows, don't use all of the batter.