Spray the crock-pot with baking spray.
Mix 1 cup brown sugar, flour, 3 tablespoons cocoa, baking powder and salt in a mixing bowl. Stir in milk, margarine and vanilla. Spoon batter into bottom of crock pot (dough is very thick).
In another bowl, mix together 3/4 cup brown sugar and 1/4 cup cocoa. Sprinkle evenly over batter. Do not stir.
Pour boiling water over the top. Do not stir. Cover and cook on high for 2-1/2 to 3 hours or until the cake pulls away from the sides of the crock-pot (pudding will be bubbling through).
Serve immediately with ice cream or whipped topping if desired. Or let set for 10 minutes and then invert onto a plate. Spoon pudding left in the pot over the cake.
Utensils Needed: 3 or 3-1/2 quart crock pot