Many recipes, especially older ones, routinely begin by instructing cooks or bakers to scald their cream. This means heating it to a temperature near boiling, an important safety step in the days before widespread pasteurization. Although cream is now routinely pasteurized for safety, scalding it is still useful in some circumstances. It kills any bacteria that have recolonized the cream since it was pasteurized, and provides a useful opportunity to infuse the cream with flavors. Cream scorches easily, but there are several ways to heat it without damaging its flavor.
Heat the cream gently in a heavy, wide-bottomed saucepan over low to moderate heat. It can take 30 minutes or longer for the cream to rise to a simmering temperature of over 180 degrees Fahrenheit, so be patient. Stir it frequently with a soft silicon spatula to prevent sticking and scorching. This is the best technique when you want to infuse spices or vanilla beans into the cream.
Pour the cream into a double boiler and set it over a pot of boiling water. If you don't have a double boiler, improvise by finding a mixing bowl that will rest neatly on top of the pot of water. This indirect heat will eventually bring your cream to a simmer, but with much less risk of scorching.
Measure your cream into a microwave-safe glass bowl or measuring cup, and place it in the microwave. Heat it at full power in one-minute increments, until it's hot to the touch. Stir the cream with a clean spoon and continue heating, 30 seconds at a time. When the cream begins to bubble, stop the microwave and remove the cream. Don't fill your bowl more than half-full, because if you overheat the cream, it will foam up dramatically.
Steam the cream using the milk-frothing attachment of your cappuccino machine, or a standalone steam-type milk frother. This method is very fast, but provides minimal opportunity for infusing flavors.