¼ cup (½ stick) unsalted butter

1 vanilla bean, split lengthwise

¾ cup (packed) light brown sugar

2 ½ cups heavy cream

1 cup whole milk

1 tablespoon bourbon or Scotch

½ teaspoon kosher salt

6 large egg yolks

¼ cup cornstarch

3 tablespoon sugar

Crème fraîche and crushed gingersnap cookies (for serving; optional)

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. 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. Top with creme fraiche and crushed cookies to serve.