Lack of self-control is at the heart of many undesirable behaviors, such as overeating, overspending, and even overworking. While the field of Persuasive Technologies searches for ways to change attitudes and behaviors, it often neglects the science of self-control. We present the Chocolate Machine, an exploratory interactive product to train self-control strength based upon Ego Depletion theory. A field study showed the machine to increase perceived self-control over time, while providing a sustained positive experience. This makes the machine transformational, aiming at facilitating behaviors people find worthwhile, but hard to implement.