Many doctored cake recipes call for adding instant pudding mix to a boxed cake mix for a better result, but cook-and-serve pudding mixes work just as well. After all, the two have almost identical ingredients -- sugar, cornstarch, flavorings and perhaps food dyes. Cook-and-serve pudding mixes contain dextrose and some regular cornstarch, while instant mixes contain only modified cornstarch, all of which are thickening agents. Go ahead and use whichever one you have on hand.
Benefits
Whether you're using cook-and-serve or instant pudding mix, both add flavor, texture and moisture to a cake. Pudding mixes also create a firmer, more stable result, which is especially important if you want to decorate the cake. Pudding helps suspend chocolate chips, fruit or nuts so they don't sink to the bottom. Cakes made with pudding mixes may also stay fresher for longer.
Method
Use a package of pudding mix just as you would instant pudding mix. Simply combine the mix with the dry ingredients. If you're using a boxed cake mix, stir the pudding into the dry cake mix before you add the eggs, oil and water. If you're making a cake from scratch, mix the pudding in when you add the flour.
Varieties
Regular pudding mix adds flavor to almost any type of cake. Add lemon pudding to a lemon or citrus-flavored cake. Chocolate pudding creates a richer chocolate cake, while banana pudding does the same for banana cake. Vanilla pudding has a neutral flavor that pairs well with almost any type of cake. Pudding mixes work best in cake recipes that are meant to be moist, such as Bundt cakes, fruitcakes and rich chocolate or vanilla cakes. Don't limit it to cakes, though. It works just as well in quick breads. Try pudding mix in pumpkin, banana or lemon bread. Don't use pudding mixes in firm, slightly dry pound cakes or lighter-than-air angel food cakes. Pudding mix will make these cakes too dense and moist.
Storage
Although pudding cakes stay moister than regular cakes, they will still dry out if improperly stored. Moist, dense cakes are best wrapped in plastic wrap and stored at room temperature. Eat them within two days or freeze the leftovers. Refrigerating cake tends to make it dry and taste stale. Keep in mind that if the cake has a perishable frosting, such as one containing whipping cream or cream cheese, it must be refrigerated.
References
Cake Mix Doctor: Southern Caramel Cake with Peach Conserve