Heat the milk in a small saucepan set over medium heat, just until it starts to steam.
In a small heat-proof bowl, whisk together the egg yolks, sugar, and cornstarch for 1 minute, or until they become pale yellow.
Next, slowly whisk in the milk, a little at a time. Make sure not to add it all at once or you may scramble the eggs.
Once all of the milk has been incorporated, return the egg mixture to the saucepan and set it over medium heat again.
Cook, stirring constantly, for 3-4 minutes or until the cream has thickened. It will be very thin and then thicken very quickly-- don’t stop stirring or it may burn.
Once the cream has thickened, remove it from the heat and add the vanilla bean paste and butter. Whisk to combine.
Transfer the cream to an airtight container and cover the surface with plastic wrap (make sure the plastic is directly touching the cream so it doesn’t form a skin).
Transfer the cream to the fridge and chill until it is no longer hot-- about 1 hour.