Monthly Feature: The weight of air is a phenomenon most cooks seldom contemplate. But if you live in Denver, Calgary, Johannesburg, or a host of other high-altitude locales, you'll face fallen cakes and overflowing batters if you don't. As elevation rises, air pressure falls, which means that bakers living at 3,000 feet (1,000 meters) will see different results than lowland bakers. Since most recipes are designed for sea level, high-altitude success requires a few clever adjustments. Low air pr...