Simple, simple...
And no gelatin!
Once cooked, the condensed milk should be added to the egg yolks while still hot.
This way, the heat from the condensed milk will coagulate the proteins in the egg yolks and give body to the mousse.
This way, you will get a thicker mousse and if you carefully fold in the egg whites, the mousse will not separate as is the case in other places.
Enjoy!