Of all the foods that have become available in shelf-stable containers on supermarket shelves, the one that has most puzzled me is chai. I’m always astonished to see it and even more surprised when I hear people wonder what is in it. “Chai” is simply the Indian term for tea and refers to black tea, with milk, sugar and a few spices. There are countless variations but one truth runs through them all: It is always better, cheaper and more nutritious when you make it at home. And it is so easy to do so. If you really love it, use this recipe to make a batch that will last two or three days. Simply reheat it, cup by cup, as you like. In warm weather, you can serve it over ice if you like.