Heat the sesame until fragrant in a dry frying pan.
Ground the seeds in a mortal and pestle and reserve.
Place the milk and the vanilla essence in a medium heavy-based saucepan.
Heat over a low heat, stirring occasionally until the milk just comes to the boil.
Remove from heat and set aside.
beat the egg yolks and sugar in a heatproof bowl until thick and pale.
Very gradually stir the milk into the egg mixture.
Place the heatproof bowl over a saucepan of simmering water. Don't allow the bowl to touch the water as the eggs will scramble.
Cook, stirring constantly, for 25 minutes or until the custard coats the back of the spoon.
Stir through the sesame and freeze until almost frozen.
Use a stick blender to beat the ice-cream every 2 hours for 2 or 3 times to break up ice crystals as they form.