Rinse the 1 cup dried corn and pick through. Discard any rocks or dirt or debris. Soak corn in cold water overnight.
The next day, drain and rinse the corn. Place in a large pot and fill the pot with water. Add the 1/4 cup salt and 1/2 onion.
Bring to a boil over high heat. Reduce the heat so it is gently simmering. Let simmer until corn is tender but retains some bite. It should be al dente, like pasta. This can take anywhere from 1-2 hours.
Drain and discard onion. Corn is now ready to use in pozole or your favorite recipe.
If not using right away, store in an airtight container in the fridge for up to a week or in the freezer for up to 6 months.