In a large mixing bowl, dissolve yeast in water. Add sugar, salt, egg, butter and 1 cup of the flour. Beat until smooth. Add enough remaining flour to form a soft dough. Turn onto a floured board. Knead until smooth and elastic, about 3-5 minutes. Place in a greased bowl, turning once to grease top. Cover and let rest for 20 minutes. Punch dough down. Press into the bottom and up the sides of a greased 15x10x1 inch baking pan. In a large mixing bowl, beat cream cheese until smooth. Gradually add cocoa and sugar. Beat until fluffy. Beat in eggs, one at a time. Add vanilla. Pour into crust. Bake at 180ºC . for 20-25 minutes or until crust is golden brown. Cool. In a saucepan, combine first four topping ingredients. Cook over Low heat until thick, about 8-10 minutes, stirring constantly. Remove from the heat, stir in vanilla, coconut and nuts. Spread over cooled cake. Chill at least 1 hour. Store in refrigerator.