In a mixing bowl, whisk together the egg yolks, vanilla extract, granulated sugar, salt, cornstarch and softened butter. Once everything is mixed together set aside.
Milk mixture:
In a medium sauce pan over medium-low heat, heat the milk and heavy cream. Once bubbles start to form turn off the heat.
Tempering the egg mixture:
Whisk in 1/4 cup of the milk mixture into the egg mixture. Whisk it in slowly.
Once the egg yolks have been tempered, return the mixture to the pot with the milk.
Assembly:
Place the sauce pan back on the heat and let it thicken for 5-10 minutes. Be sure to stir it regularly.
Once the sauce has thicken remove from the heat and pour into a bowl. To ensure you have no lumps, I highly recommend straining the mixture into a bowl.
Refrigerate:
Place a serum wrap over the mixture, making sure to stick it to the pudding to prevent the development of a skin.