A café breve is an espresso drink made with half-and-half — equal parts milk and cream — instead of milk.
What changes
Far more fat. The result is thicker, richer and noticeably sweeter, with a heavier mouthfeel and a foam that is denser and more stable.
It is essentially a latte with the volume turned up.
Steaming it
Higher fat foams differently: it takes air less readily and holds it more stably. Stretch a little longer than you would for milk, and stop cooler — around 55 to 60 °C, since the higher fat scorches sooner.
The name
Breve means short in Italian and Spanish, and the drink is not Italian. It is an American coffee-shop invention, and the name appears to have been chosen for sound rather than meaning.
The honest note
It is very rich — roughly double the fat of a latte the same size. That is the point, and it is a dessert as much as a coffee.
Making one
A double espresso and 150 to 200 ml of steamed half-and-half.