Place a rubber spatula and a whisk on a plate next to the stovetop to have them ready to use interchangeably.
Pour the heavy cream (500 g; 17.6 oz) in a large bowl and set a fine-mesh sieve over it; set aside.
Prepare the egg yolks: put the egg yolks (5 egg yolks) in a medium bowl, and whisk them lightly to break them down. Set the bowl next to the stovetop.
Warm the milk and the sugar: place the milk (400 g; 14.1 oz) and the sugar (185 g; 6.5 oz) in a medium saucepan. Warm over medium heat, often stirring, until the sugar dissolves.
Pour the warm milk into the egg yolks: when all the sugar dissolves and the milk is hot and steamy, remove it from the heat and slowly pour roughly half of the warm milk over the egg yolks with one hand while whisking them vigorously with the other hand to temper them.
Cook until thickened: pour the tempered yolks & milk back into the saucepan and over medium-high heat. Cook, constantly stirring with a rubber spatula and scraping the bottom of the saucepan to prevent the custard from scalding. Maintain a medium temperature, do not let it come to a boil.
Remove from the heat when the custard starts to thicken (82ºC / 179 ºF / when it thickens to coat the back of a spoon / when you tilt the saucepan, a layer of thickened custard appears to form on the bottom).
Pour the thickened milk through the fine-mesh sieve and into the heavy cream; stir to combine.
Scrape the vanilla seeds from the vanilla bean into the mixture; whisk vigorously to distribute the seeds. Αdd the vanilla bean in, too.