In a medium saucepan, combine the drained beans, onion, garlic, and thyme. Add enough cold water to cover by 2 inches. Bring to a boil over high heat. Reduce the heat to medium-low and simmer for 20 minutes. Season with the salt and continue cooking until the beans are just tender, about 15 minutes more, depending on the dryness of the beans. Drain the beans, reserving 1/2 cup of the cooking liquid.

Return the beans and the reserved liquid to the saucepan. Add the cream and bring to a simmer over medium heat. Cook until slightly thickened, about 5 minutes. Stir in the butter, and season with salt and pepper.