In the mixing bowl whisk egg yolks with half of the sugar and set aside.
In the medium saucepan, add milk and remaining sugar and warm up over medium heat. Do not boil!
Gradually, while whisking constantly, add hot milk into egg yolks.
When all incorporated, pour mixture back to saucepan. Continue whisking, cook until mixture is thick and pudding consistency.
Transfer cream to a medium bowl. Cover with plastic wrap “to contact” and let cool in the refrigerator.
When you are ready to assemble cake, whip room temperature unsalted butter.
Add custard cream a few spoons at the time and keep whisking. Cream should be smooth and soft. Important: cream and butter should be room temperature.