Position a rack in the center of the oven, set a rimmed baking sheet on the rack, and heat the oven to 425°F.
In a medium saucepan, bring the milk, cream, vanilla bean, and scraped seeds to a boil. Remove from the heat and let the mixture steep for 20 minutes.
Remove the vanilla bean from the milk and cream, scraping off any residual seeds into the milk. Return the pan to medium heat until the milk is hot but not boiling, about 2 minutes. Turn off the heat, leaving the pan on the burner. Whisk in the pumpkin, brown sugar, salt, cinnamon, and nutmeg until smooth. One at a time, add the eggs, whisking constantly. Stir in the bourbon.
Pour the filling into the pie shell and put the pie on the hot baking sheet in the oven. Bake for 10 minutes and then reduce the oven temperature to 350°F. Bake until the center of the pie no longer wobbles when the pan is nudged (a slight jiggle is fine) 30 to 35 minutes more. Transfer the pie to a rack and let it cool completely before serving.
The step of steeping the vanilla bean in the milk and cream can be done a day ahead to intensify flavor. Simply reheat the milk gently the next day and continue with the recipe.
Serve with lightly sweetened whipped cream.