Chocolate Eclair Cake

Beat pudding and milk until thick. Add Cool Whip and blend together well. Using a 9 x 13 pan, place a single layer of graham crackers on bottom of pan. Carefully spread 1/2 the pudding mixture on the crackers. Place another layer of crackers on the pudding. Spread the rest of the pudding on this layer. Finish with a final layer of crackers. Spread icing on top and refrigerate overnight. Bring cocoa and milk to a boil and cook for 1 minute. Add butter and vanilla, blending well. Remove from heat and beat until thick. Carefully spread quickly on cake.