Brazilian Avocado Ice Cream
Lime juice can be used in place of the lemon, if desired. Light whipping cream can be used in place of the half-and-half.
If using an ice cream maker with an open top such a Cuisinart(R), put a towel over the top while it is mixing to hold the cold air in.
I have not tried this, but I heard that if the ingredients are cold before going into the machine, they will become ice cream faster, so you could try putting the mixing bowl in the refrigerator for a few minutes.
If your ice cream is not firm enough after three hours, overnight in the freezer will do the trick.