Make a light roux. Melt the 3 tablespoons of butter, blend in the flour and stir over moderate heat for 2 minutes to cook the flour without browning. Remove from heat and when the roux has stopped bubbling, vigorously blend in all the hot milk at once with wire whip, beating until mixture is perfectly smooth.

Blend in the 3/4 cup of cream, the herb, garlic, salt and pepper. Return to moderately high heat, stirring with whip as sauce thickens and comes to the boil. Simmer 2 minutes, then fold in the potatoes. Sauce should just cover the potatoes; add a little more cream or milk if necessary.

Bring to simmer, correct seasoning, cover pan and simmer very slowly for 10 to 15 minutes. until potatoes are tender.

Stir up gently from bottom once or twice to be sure potatoes are not sticking; they will have absorbed half of the liquid before they are done and if sauce seems too thick you may always add a little more milk.

Reheat potatoes just before serving. Carefully correct seasoning. Gently fold in the butter and 2/3 of the herbs with a rubber spatula. Turn into a lightly buttered vegetable dish, decorate with the remaining herbs and serve at once.