An easy – and very good – side dish that goes especially well with lamb. It can also be made ahead, kept refrigerated, and then reheated at the last minute in the oven or microwave.
Cook the beans according to the package directions; drain and set aside.
In the same saucepan, melt the butter. Add the onion and saute over medium heat until limp, about 3 minutes. Stir in the flour, salt, and pepper. Then add the broth, parsley, vinegar, and dill. Cook, stirring constantly, until the sauce is thick and bubbling. Reduce the heat to low and stir in the sour cream. Add the drained beans. Continue to cook until the beans are heated through, but do not boil.
If you want to make this dish in advance, pour the bean mixture into an 8-inch square glass baking dish. Before serving, heat in a microwave on high for about 10 minutes, stirring every few minutes. Or place in a preheated 350 degrees F oven for about 45 minutes, stirring occasionally, until heated through.