Preheat broiler.
Arrange chicken on broiler pan.
For sauce:
Combine Dijon mustard, sugar, vinegar, sour cream, chives and dill in a small bowl, mix well and set aside half.
Spoon one-fourth of the sauce over the chicken.
Broil for 10 minutes.
Turn the chicken.
Spoon remaining sauce over chicken.
Top with lemon slices.
Broil until juices run clear when meat is pierced, about 15 minutes.
Remove lemon slices.
Serve chicken with reserved sauce.