This pastry cream is the perfect addition to fruit tarts.
Place milk, vanilla bean, and 1/4 cup sugar in a medium saucepan over high heat; cook until almost boiling.
In a medium bowl, whisk together egg yolks with remaining 1 tablespoon sugar until thickened. Sprinkle in cornstarch and flour and continue beating until well combined.
Remove vanilla bean from milk. While whisking constantly, slowly pour heated-milk mixture into egg-yolk mixture. Pour mixture through a fine sieve back into saucepan, and cook, whisking constantly, over medium-high heat, until it thickens and registers 160 degrees on an instant-read thermometer, about 2 minutes.
Transfer to a large bowl and whisk in butter until melted. Cover with plastic wrap, pressing it directly on the surface of the pastry cream; refrigerate until completely cooled.