Now sadly out of print, this rare 1982 history of Normandy before 1066, is superb - great attention given to the sources.
It traces the duchy from its’ time under Rollo, arguing strongly that most Scandinavian aspects of rule and culture were lost; instead many Carolingian features of the area survived.
Of particular interest is the attempt to trace the lineages of key Norman families, who would come to dominate in post 1066 England.
The pre-1066 history of Normandy is very relevant to the study of post 1066 Government, Church and control in England.
Thoroughly enjoyable.