Place a rubber spatula and a whisk on a plate next to the stovetop to have them ready to use interchangeably.
Prepare the egg yolks: put the egg yolks (80 gr; 2.8 oz.) 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 (475 gr; 16.8 oz) and the sugar (90 gr; 3.2 oz.) in a medium saucepan. Warm over medium heat, often stirring, until the sugar dissolves.
Pour the hot milk into the egg yolks: when all the sugar dissolves and the milk is hot and steamy, remove it from the heat and slowly ladle the hot 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 bring it over medium-high heat. Cook, constantly stirring with a rubber spatula and scraping the bottom of the saucepan to prevent the custard from scalding. Do not let it come to a boil.
Remove from the heat when the custard starts to thicken slightly (80ºC / 176 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 it into a heatproof blender jag.
Add the chopped white chocolate (200 gr; 7 oz.) and leave it to sit for one minute.
Blend until smooth, pausing once to scrape with the rubber spatula any white chocolate stuck on the insides of the jag.
Add the heavy cream (355 gr; 12.5 oz.) and blend to combine.