This isn’t really cheating because the sugar that goes into concentrated milk has been caramelized.
It’s just a matter of making life simple by taking advantage of its creamy consistency. This is a requisite for Banoffee Pie, as well as many other recipes in this book. Watch out for spattering.
It’s unwise to heat the condensed milk in its can in a pan of water. If you become absorbed in something else, the pan may run dry and the can could explode. It’s safer and quicker to do the job in a microwave.