You may use ground beef, Italian sausage or a combination of the two. Or you may leave it out. We have tried it all three ways and they are all really good but our favorite is the combination of ground beef and sausage.
To freeze: portion out the cooled sauce into freezer safe containers or freezer bags.
Also, if you want to skip the browning of the ground beef just add it uncooked to the slow cooker and break it up into smallish chunks. Stir in the remaining ingredients and cook as usual.