Combine strawberries and sugar in a 13x9x2" baking pan. Scrape in seeds from vanilla bean and add pod; toss to combine. Roast berries, stirring occasionally, until juices are bubbling, 15-20 minutes.
Let cool.
Discard pod. Purée berries, buttermilk, sour cream, and salt in a blender until smooth. Process mixture in an ice cream maker according to manufacturer's instructions.
Transfer sherbet to an airtight container and freeze until ready to serve.
DO AHEAD: Sherbet can be made 1 week ahead. Keep frozen.
Let soften at room temperature 15 minutes before serving.
