Bourbon-Butterscotch Pudding

Melt butter in a medium saucepan over medium heat. Scrape in seeds from vanilla bean; add bean. Cook, swirling pan occasionally, until butter begins to brown and smell nutty, about 3 minutes. Add brown sugar and cook, stirring occasionally, until sugar is starting to dissolve, about 2 minutes. Add cream, milk, bourbon, and salt; bring to a simmer. Remove from heat. Whisk egg yolks, cornstarch, and sugar in a large bowl until smooth. Gradually add hot cream mixture, whisking constantly. Wipe out saucepan. Strain custard through a fine-mesh sieve back into saucepan and cook over medium heat, stirring often, until custard bubbles occasionally and starts to thicken, 5-6 minutes. Remove saucepan from heat and transfer mixture to a blender. Blend briefly on low speed until smooth. Place ramekins or bowls on a rimmed baking sheet. Divide custard evenly among ramekins and chill until set, at least 3 hours. DO AHEAD: Puddings can be made 3 days ahead. Cover and keep chilled. Top each pudding with crème fraîche and crushed gingersnaps, if desired.