Maangchi's Myeolchi-Dasima-Gukmul, or anchovy-kelp stock, is great to make in big batches, and can be stored in the freezer for up to 3 months.
In a large pot with a lid, add 4 1/2 quarts water, the radish, onion, scallions, anchovies, and kombu. Bring to a boil over medium-high heat, partially cover, and cook until the vegetables and kombu are tender, about 30 minutes.
Reduce heat to medium and continue to cook at a low boil, with lid ajar, until the radish is translucent and the broth is fragrant, about 45 minutes.
Reduce heat to low and simmer, with lid ajar, for 10 minutes. Strain through a fine-mesh strainer into a large bowl. Let cool. Stock can be stored in airtight containers in the refrigerator for up to 1 week or in the freezer for up to 3 months.