Place chicken in deep 10-inch skillet. Add broth and 4 cups water. Bring to boiling. Reduce heat to low; simmer, turning over once, until no longer pink near bone, 20 minutes. Remove from skillet. When cool enough to handle, pull into small pieces; place in bowl. Discard skin, bones.
Cook pasta according to package directions. Add broccoli for last 7 minutes.
Drain pasta and broccoli; rinse under cold water. Drain. Add to chicken. Add onion.
Mix mayonnaise, sour cream, mustard, vinegar, sugar, tarragon, salt and pepper in bowl. Fold into salad. Cover; refrigerate until serving. Makes 12 servings.