Mix the passionfruit juice with the cream, the egg yolk, the sugar and the cornstarch.
Mix this well and then while stirring bring it to a simmer to thicken the cremeux. Now with big recipes I prefer to first bring the liquid to a simmer and add it to the starch and egg yolk, but with small quantities you can just mix it all and do it all at once.
Then transfer the white chocolate into a bowl and pour the hot cremeux on top. Now blend it till smooth and fully emulsified. Then cover it and keep it in your fridge for later. Once cold it has the perfect texture.