In a medium saucepan, heat milks and ¼ cup (50 grams) sugar over medium heat, whisking frequently, until steaming. (Do not boil.)

In a medium bowl, whisk together egg yolks, cornstarch, salt, and remaining ¼ cup (50 grams) sugar. Gradually add hot milk mixture, whisking constantly. Pour egg yolk mixture into saucepan; cook over medium heat, whisking constantly, until thickened and bubbly, 4 to 5 minutes. Whisk in extracts.

Strain mixture through a fine-mesh sieve into a large bowl. Whisk in butter until melted and well combined. Cover with plastic wrap, pressing wrap directly onto surface of pastry cream to prevent a skin from forming. Refrigerate until an instant-read thermometer registers 65°F (18°C) to 70°F (21°C) before using, 2½ to 3 hours.