Mix all ingredients together in crock. Cover and cook on LOW for 2 1/2 hours, whisking several times during cooking.
When cooking is complete, test to be sure it's ready using the "wooden spoon test". Dip a clean wooden spoon into the mixture, then run a clean finger over the back of the spoon (through the mixture). If your finger leaves a "trail" then the base is done. If no "trail", cook 1/2 hours more and test again.
Transfer the ice cream base to a bowl and let it cook completely in the fridge. Freeze ice cream according to ice cream freezer directions.