First, melt the lard. Oh, you said low fat? We’ll get to that in a minute. Traditionally to make refried beans, you sauté some onion (and perhaps garlic) in lard, add boiled beans and mash them to a coarse paste, and add bean stock if necessary to get the right consistency. Continue to cook until done, which is described as anywhere between soft-mashed-potato stage and almost dry.
There are a couple suggestions for making low-fat versions, although they begin to depart pretty substantially from traditional refried beans. The first move is to switch from lard (or bacon grease) to vegetable oil or olive oil and decrease the amount used. Where some recipes call for nearly half a cup of lard for four cups of beans, others cut that down – to a quarter cup or as little as 1 tablespoon. At that point, of course, you’re doing very little frying of those beans; you’re basically simmering boiled beans.
To replace some of the flavor and improve the consistency of these simmered beans, some low-fat cookbooks tell you to add a cup or so of low-fat chicken stock, and cook until you reach the mashed-potato consistency. Basically, you’re making a really thick re-warmed bean soup rather than refried beans. But that might be just fine for many of the dishes you have in mind. And for some people, the low-fat element may be more important than any sense of tradition.
Rick Bayless, in his wonderful book Mexico One Plate at a Time, provides a recipe for a “not-so-rich version of frijoles refritos” that may strike a happy balance between tradition and nutrition. He heats 1/4-cup of vegetable oil and sautés a chopped onion until deeply golden brown, adds 4 large chopped garlic cloves and sautés for another minute. Then he adds the beans to the skillet several spoonsful at a time, mashing them as he adds them. When all the beans have been added and mashed (he started with seven or eight cups of boiled beans that he made himself, while many people will just open a couple of cans), he adds enough bean stock to attain a soft consistency, and mentions that it will thicken as it cooks further and more as it cools at the table.
By the way, Diana Kennedy, an authority on Mexican cooking, has cleared up the mystery of why these are called refried beans, when they are clearly fried only once. In Mexico it is common, she says, to use the prefix “re” for emphasis, so the name frijoles refritos refers to beans that are well fried, not twice fried. In fact, in her recipe in The Cuisines of Mexico, the beans are fried until they begin to dry out and pull away from the edges of the pan. Then as a mass, they are rolled up and tipped out of the pan like an omelet, garnished with cheese, lettuce and radishes, and served with tortilla chips.