Compare two CSV files and output diffences to a new CSV

I'm trying to create a PS script that will read in two csv files and then output the differences to a new csv file.

AllShares.csv contains:

Server,Share,Sponsor

server1,share1,sponsor1

server1,share2,sponsor2

server2,share1,sponsor1

NetworkShares.csv contains:

Server,Share

server1,share1

server2,share1

server1,share2

server1,share3

Thanks