Ur-Fascism By Umberto Eco (1995) [pdf]
To complement this I recommend Five Stages of Fascism by Robert Paxton. He takes a temporal view of fascism rather than ideological, reasoning that unlike most other -isms, fascism does not have a body of works that define the ideology. On the contrary, fascist movements despise coherent philosophies.So his focus is on development of fascist movements in time.