Roasted bone marrow served on toast is one of the classic gourmet dishes with origins extending at least as far back as france in the 1600s. The modern take on the dish often involves serving the roasted bones with toast, a small heap of grey sea salt, and an herb salad. Marrow bones are generally the leg bones from either beef or veal. Asian grocery stores will almost always sell fresh marrow bones and your local supermarket might offer frozen ones. Frozen ones are fine for making soup, but if you're serving the marrow specifically, go for the fresh ones. If you don't have an asian grocery nearby, try a specialty butcher shop. When deciding between beef or veal, keep in mind that veal marrow has a much milder flavor than the beef version, which can sometimes be overpowering. Either way, ask for center-cut marrow bones. Note that often the marrow bones are cut crosswise rather than lengthwise. Serving them this way allows your guests to fully immerse themselves in the act of extracting the marrow from the bones. You can ask your butcher to saw the bones lengthwise instead for easy eating, but it's easy to overcook the marrow this way, causing it to liquefy. To serve, place the marrow bones on individual plates with toast, salad and sea salt. To eat, dig the marrow out of the bones, spread it on the toast, top with salad, and sprinkle with sea salt. It's a hands-on dish that's fun for a dinner party. This recipe serves four as an appetizer and two as a main dish.