Lighter and more delicate than the filling often used in commercial bakeries, this pastry cream lets summer fruit be the star.
Heat milk and cream in a medium saucepan over medium-low heat until it begins to simmer. Add vanilla bean pod and seeds; let sit off the heat, covered, 30 minutes.
Rewarm milk mixture over medium-high heat until almost simmering. Meanwhile, mix yolks and sugar in a medium bowl. Blend in cornstarch and salt. Slowly whisk hot milk mixture into yolk mixture, 1/2 cup at a time. Pour mixture back into pan and cook, whisking constantly, until as thick as pudding, about 4 minutes. Pour custard through a strainer into a clean bowl (discard vanilla pod).
Lay plastic wrap against surface of custard to keep a skin from forming. Chill at least 3 hours and up to 4 days.
Whisk cold custard to smoothen it, then spread or pipe into tart shell(s) and top with fruit.