Method

Rinse and trim beans. Cut each bean diagonally into 2 or 3 strips.

In heavy saucepan, melt butter; cook onions and garlic over medium heat for 1 minute. Add beans, tossing to coat with onion mixture; cook for 3 minutes. Stir in parsley. Cover, reduce heat to low and cook, stirring periodically, until beans are tender, 10 to 15 minutes. (Beans can be prepared ahead to this point, covered and refrigerated; reheat before continuing with recipe.)

Sprinkle beans with dill, and salt to taste. Lightly beat together egg yolk and sour cream. Pour over hot beans and toss just until beans are evenly coated and heated through. Taste, adjust seasoning, if necessary, and serve immediately.