Add asparagus; cover and boil for 3 minutes. meanwhile, in a small skillet, saute onion in butter until tender. Stir in the flour, garlic powder, lemon-pepper and salt until blended. Gradually stir in broth.
Add the parsley, vinegar and dill.
Bring to a boil; cook and stir 2 minutes or until thickened. Reduce heat to low; whisk in sour cream.
Drain asparagus; arrange on a serving platter. Top with cream sauce.