Heat the milk and cream in a small saucepan over medium heat until hot, taking care not to let it boil.
Whisk the egg yolks and caster sugar in a medium bowl until combined.
Whisking constantly, pour the warm milk and cream mixture over the eggs.
Return the mixture to the saucepan and cook over very low heat, stirring constantly with a wooden spoon in a figure-of-eight movement, until it thickens and coats the wooden spoon.
Remove from heat and strain the custard through a sieve into a serving jug. Stir in the vanilla essence. Serve the custard warm or cold.