Sauerampfersuppe (Sorrel Soup)

Yield:	4 Servings
Categories:	German, Soups

1	bn	Sorrel
1	bn	Fresh chervil
50	g	Butter (3 1/2 Tbsp)
3	tb	Flour
1		Yolk
4	tb	To 5 tb sour cream
1 1/2	l	Meat broth or water (approx. 1 1/2 qts)