Cook the seasonings in 2 quarts of salted water for 20 to 25 minutes: the carrots, the onion pricked with a clove, the garlic, the bouquet garni tied with the white of the leek. Add the beans, bring to a boil then lower the heat. Simmer until completely cooked, adding, if necessary, more water to make sure that the beans are always covered by an inch of liquid. Start the sauce by making a roux, with the butter and 1 full tablespoon of flour, heat, stir, then add the cream to make a thick white sauce (bÄchamel), check the seasonings, adding a pinch of freshly ground pepper. Add the fresh chopped herbs when ready to serve.
