In a skillet, fry bacon until crisp. Remove and drain on paper towels. Reserve bacon drippings in the skillet. When cool enough to handle, crumble or break up the bacon.
Sauté onion in the bacon drippings until just soft and starting to color. Add beans and cook briefly until al dente. Add vinegar and stir briefly. Turn off the heat and stir in sour cream. Do not allow to boil, or the sour cream will curdle. Add more vinegar if not quite sharp enough. Season with white pepper and chopped dill, if using. Garnish with crumbled bacon.
Serve warm or at room temperature.