Airy and sweet, this classic French sauce is the perfect filling for cream puffs or eclairs.
Whisk 2 tablespoons granulated sugar, the confectioners' sugar, salt, and egg yolks in a medium bowl. Whisk in cornstarch, 1 tablespoon at a time. Set aside.
Bring milk, vanilla bean and seeds, and remaining 2 tablespoons granulated sugar to a simmer in a medium saucepan over medium heat, stirring until sugar has dissolved. Remove bean, and discard. Whisk a third of the milk mixture into yolk mixture. Whisking constantly, gradually add remaining milk mixture. Pour back into pan; bring to a boil, whisking constantly. Cook, whisking, until thick, 2 to 3 minutes. Remove from heat; whisk in butter.
Pour through a sieve into a bowl; discard solids. Cover with plastic wrap, pressing it directly onto surface. Refrigerate pastry cream until cold, about 2 hours (up to 3 days); beat until smooth before using.
Beat cream until soft peaks form. Whisk half the whipped cream into the pastry cream; fold in remaining whipped cream.