Gather the ingredients.
In a large saucepan, bring the half-and-half to a simmer over medium-high heat.
In a medium-sized bowl, whisk together the egg yolks, cornstarch, sugar, and salt until smooth.
Add half of the scalded milk to the bowl containing the eggs, constantly whisking to incorporate.
Return the entire mixture to the saucepan containing the remaining milk, whisking over moderate heat.
Continue whisking for about 2 to 5 minutes, until the mixture is thickened and begins to simmer.
Allow the pastry cream to simmer, whisking for an additional 2 minutes.
Remove from the heat and whisk in the vanilla and cold, unsalted butter.
Transfer to another bowl and allow it to cool completely.
Cover and refrigerate for at least 5 hours or up to three days before using.