I sometimes add vanilla after cooking since vanilla contains alcohol and that will boil off when heated. The stove-top recipe does this. Cool and serve. For skim milk, and because I used it as dinner last night, I used 2 eggs. Egg substitute could also be used.
Egg yolk is a thickener as is the tapioca itself.
Stove Top Version Follow recipe above but put everything except vanilla into a double boiler. Bring mixture to a full boil. A full boil is when it is rolling up all over the pot. Remove from heat and cool for 20 minutes. Stir in vanilla.