Why Does Pie Meringue Shrink?
two things that will prevent the shrinkage/separation:
- make sure you put the meringue on the pie when the filling is still hot, so that the residual heat can start cooking the base of the meringue, which will discourage shrinking
- when you mound it onto the pie, be sure to seal it completely against the crust - use your spatula to spread/press it lightly against the edges.
The method least prone to failure in my experience is to use an italian meringue - Very stable. you make a sugar syrup and then drizzle it into the egg whites as you are beating them.
Here are instructions from Cooks Country that don't require a thermometer, but you do have to register.