Rinse and pick over peas.
Cover with water and leave to soak overnight.
Next morning, drain, add remaining ingredients, and bring to boil.
Cover pot, turn down heat, and simmer for about 2 hours, stirring occasionally.
When peas are tender, remove ham bone or knuckle, cut meat from bone, and return to pot.
Take out herb sprigs.
Puree if desired, reheat, and serve in individual bowls, each topped with a small pat of butter.