A little bit of whisking is all you need to prevent grainy pudding.
While developing our recipe for Best Butterscotch Pudding (see related content), we noticed that some batches turned out slightly grainy, while others were silky smooth. The problem, we were surprised to learn, wasn’t undissolved cornstarch: It was the butter. Once the pudding cooled and the fat solidified, any bits that hadn’t been thoroughly broken down came across as grainy on the tongue. Vigorously whisking the pudding—or any custard with a generous amount of butter—breaks down the fat into tiny droplets that are too small to detect once the mixture cools. (It’s the same principle as emulsifying a vinaigrette: Thoroughly whisking in the oil ensures that the fat breaks down into tiny droplets that don’t “break” the dressing.)