In a medium bowl, whisk together egg yolks, sugar, cornstarch, and salt.

In a small saucepan, heat half-and-half over low heat, stirring frequently, just until steaming. (Do not boil.) Slowly add half of half-and-half to egg yolk mixture, whisking constantly. Add egg mixture to remaining half-and-half in pan. Bring to a boil, whisking constantly; cook, whisking constantly, until thickened, 2 to 3 minutes. Remove from heat. Whisk in butter and vanilla. Cover with plastic wrap, pressing wrap directly on surface of custard to prevent a skin from forming. Refrigerate until cold, at least 30 minutes.

In the bowl of a stand mixer fitted with the whisk attachment, beat cold cream at medium-high speed until medium-stiff peaks form. Add cold custard, and beat until combined and fluffy, stopping to scrape sides of bowl. Use immediately.