Sagolguk is a key broth in Korean food, which you can eat simply as an accompaniment with spicier dishes (like a dolsotbibimbap) - dress simply with green onions and salt, or use as the basis of other soups, like dduk guk, dduk mandu guk, seolleongtang and other soup recipes. It is made from beef bones and takes a long time to cook.
1 package of beef soup bone (4-5 lb) -- most Asian groceries carry bones cut thinner than regular American grocery chains
1 large round onion, peeled & whole
2-3 stalks green onion
salt and pepper to taste
2 large jars, 1 gallon or bigger
Put bones in a pot filled with cold water; soak it for ½ - 1 hr to get blood out.
Discard the water, and add enough new water to cover the bones. Bring this to a boil. As soon as it begins boiling, turn the heat off and let it cool. Drain, then discard the water and wash off dark residues from the bone.
Add new water to cover the bone and put the whole onion in – it adds savory smell to the soup. Bring to a boil, and turn the heat to medium – keep boiling, adding more water to cover the bones as the water level goes lower. Repeat this process for about 2-3 hours, or until the liquid turns milky white. Remove from heat, drain the milky liquid into a jar.
Then add more water to cover the bones, and repeat the same process.
You can boil the bones for 6-8 hours over a period of 2 days. You should be able to get 2 gallon jars of milky white bone soup. There should be some white, gelatin-like stuff coming out from the bone. You can serve this along with the soup.
Let the stock cool, then refrigerate. After a few hours, there should be a hard layer of fat formed on top - you can remove this and discard. You can save this soup stock for a long time if you freeze it. Use it as you need it - divide it into small portions and freeze, for basic stock for dduk guk, dduk mandoo guk, seolleongtang and other soup recipes, or you can serve this soup simply with salt, pepper and garnish with chopped green onion.