Dissolve jello in 0.75 c boiling water. Add half c cold water and set aside at room temp.
Mix and bake cake as directed in 9x13 pan. Cool 20-25 mins. Poke holes in cake with end of wooden spoon, about 4 cm apart. With cup, slowly pour jello mixture into holes.
Refrigerate cake and prepare topping. In chilled bowl, blend whipped topping mix, pudding, cold milk and vanilla til stiff, 3-8 minutes.
Immediately frost cake. Store in refrigerator and serve chilled.