Rinse and dry beans and remove any stones. Add beans and 2 inches water to a pot and boil 2 minutes. Take pot off of heat and let stand with lid on pot for 1 hour. Strain beans and cover with 2 inches of water and bring to a boil. Lower heat and simmer with lid on 1 1/2 to 2 hours or until beans are soft. Strain, saving 2 cups liquid.
Heat a cooking spray coated frying pan over medium heat. Cook onions 3 to 5 minutes. Combine 1 cup beans and 1 cup saved liquid and cook over high heat, smashing beans until smooth. Mix in half the remaining beans and liquid and cook more, while mashing beans. Continue with the rest of the beans and liquid. Sprinkle with salt and pepper.