Combine brown sugar, egg, and butter in a saucepan over low heat; bring to a boil and cook one minute. Remove from heat and quickly stir in cracker crumbs, coconut, and nuts. Immediately press into a greased 8"x8" baking pan. Chill until firm. Spread with Buttery Cocoa Frosting; chill again until firm. Cut into squares.
Butter Cocoa Frosting:
Melt butter in a saucepan over low heat. Stir in water, vanilla, cocoa and enough powdered sugar to reach desired spreading consistency.