Step 1

Preheat oven to 425°. Combine strawberries and sugar in a 13x9x2 inches 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.

Step 2

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.

Step 3

DO AHEAD: Sherbet can be made 1 week ahead. Keep frozen. Let soften at room temperature 15 minutes before serving.