In a medium saucepan, pour in the full cream and add the halved vanilla bean along with its seeds. Heat over medium heat until barely simmering, then remove from heat and let infuse for 10-15 minutes.

While the milk is infusing, whisk together the egg yolks and caster sugar in a heatproof bowl until combined and pale in color.

Slowly pour the hot milk mixture into the bowl with the egg yolks while whisking continuously to prevent curdling. Scrape in the seeds for added flavor.

Return the combined mixture to the saucepan and cook over low to medium-low heat, stirring constantly until the custard thickens (about 5-7 minutes).

To achieve a smoother texture, strain the mixture through a fine-mesh sieve into a clean bowl.

Transfer the custard sauce into a container, pressing plastic wrap against the surface to prevent skin from forming. Let it cool before refrigerating.