Why Cream and Not Milk or Half-and-Half?

Beginning cooks sometimes try to lighten recipes by replacing the cream with milk or half-and-half. The problem with this approach is that the emulsifiers in milk and half-and-half lose their ability to emulsify when they are exposed to heat or to various foods, including acidic ingredients and especially certain vegetables such as artichokes. Cream, on the other hand, is relatively stable and can be boiled, uncovered, until it reduces and thickens. To replace cream in a recipe with milk, the milk has to be stabilized with an emulsifier, like flour (in the form of roux), or with a vegetable puree, such as potato.