Another dish in which "prep" and cooking time/temp can make a world of difference. I learned from my Dad (not my Mom) to cut calves' (or lamb) liver in strips, let in spend a while in a marinade of olive oil, lemon juice, garlic, cominos, salt and pepper, skewer it, then sear in very briefly to rare or medium rare over as hot a fire as possible. Works well for hearts too, although they, tougher, profit from a longer period in the marinade (overnight's not too long).

Quick cooking seems to prevent the breakdown of some of the complex organic compounds (with bad smell and taste) present in organ meats. With kidneys, it's tough to mask or overcome that ever-present hint of what went on within them....