1 large box vanilla instant pudding
3 ½ c. milk
8 oz. sour cream
1 small can (14 oz.) sweetened condensed milk
1 T. vanilla
1 (8 oz.) whipped topping, thawed
1 box graham crackers
1 (16-oz.) container prepared chocolate frosting
Mix the instant vanilla pudding, milk, sour cream, condensed milk, and vanilla with an electric mixer until it thickens just a little bit (about 2 minutes of mixing). Add the thawed whipped topping, and mix it in with a spatula. Don't use the electric mixer here. Cover the bottom of a 10x13x2 casserole dish with a layer of graham crackers. (Or you could use two 9-inch square dishes.) Pour about half of the pudding mixture onto the crackers. Add a second layer of graham crackers, pour on the rest of the pudding, then add a top layer of crackers.
Microwave the container of frosting (50% power for 2 minutes), mix with a spoon, then pour onto the top layer of crackers. Refrigerate. It's best the next day.