How to heat milk without scalding?
While living France, I noticed the French using a milk watcher while cooking their milk in order to avoid this very thing.
Glass Milk Watcher
The above glass milk watcher is the one I am personally familiar with.
How it works
Normally, boiling water does not boil over. When fats, starches, and some other substances are present in boiling water, for example by adding milk or pasta, boiling over can occur. A film forms on the surface of the boiling liquid; for example, cream can boil over as milk fat separates from the milk. The increased viscosity of the liquid causes the steam bubbles to form foam trapped under the film, pushing the film up and over the lip of the pot, boiling over. A milk watcher disrupts this process by collecting small bubbles of steam into one large bubble and releasing it in a manner which may puncture the surface film. The device also rattles when boiling occurs, alerting the cook who may then lower the heat setting of the stove.
By circulating fluid around the bottom of the pot the device may also prevent material from being deposited and eventually burned on the pot's bottom.