Step 1

Whisk together sugar, cornstarch, and salt in a medium saucepan. Whisk together milk and egg yolks in a glass measuring cup; add to saucepan along with butter and bring to a boil over medium heat. Let boil 1 minute, still whisking; then remove from heat and stir in vanilla.

Step 2

Strain pastry cream through a fine-mesh sieve into a bowl. Cover with plastic wrap, pressing it directly onto surface of cream to prevent skin from forming. Refrigerate until chilled, at least 2 hours and up to 2 days. Just before using, whisk until smooth.