Place beans in a heavy-based saucepan with enough water to cover.
Bring to the boil and allow to simmer for 10 - 15 minutes or until tender.
Drain and set aside. Heat the butter in another heavy-based saucepan.
Add the onion and sauté until onion is translucent.
Stir in the flour and salt.
Gradually add the sour cream while stirring.
Bring to the boil and add the beans, herbs and pepper.
Heat through and serve.