Rinse beans in cold water. Drain.
Cover with two inches of cold water and soak 12 hours. Drain.
Place beans in a large pot. Cover with 5 cups of cold water. Bring to a boil. Remove white foam.
Cover, reduce heat and simmer until tender about 2 hours (stirring occasionally). When almost done, add salt.
Drain. Reserve liquid for thinning.
Mash beans well. Add some of the saved liquid until the mashed beans have the consistency of thick sour cream.
Note: Fresh minced garlic is strong. Sautéed garlic cloves are milder.
Mash in minced garlic (or sautéed garlic) a little at a time. Taste after each addition. Salt and pepper to taste.
Sauté onions until golden.