Reduce heat to low or medium-low to keep at a slow boil
Boil gently, partially covered for about 1 1/2 hours or until beans are tender, but firm "al dente". Check after 1 hour to ensure too much water hasn't evaporated. Add more if needed. Add 2 teaspoons salt during last 30 minutes of cooking time. Once cooked, set pot aside at room temperature and keep beans in their cooking liquid until ready to use.
Add chopped onion and saute for 2-3 minutes, until slightly softened
Immediately add 2 1/2 cups of bean cooking liquid, 2 cups uncooked rice, and 1 teaspoon salt
Adjust salt as needed
The beans can be cooked and left in their cooking liquid hours or a couple of days before making the Gallo Pinto, which would then turn this dish into a simple 30 minute meal.