Put vanilla bean on a foil-lined baking sheet set on a wire rack. Toast vanilla bean with a kitchen torch, turning occasionally, until lightly charred and starting to smoke, about 30 seconds. Let cool 5 minutes. Split vanilla bean lengthwise.

Combine split vanilla bean and brandy in a medium saucepan. Carefully bring to a simmer over medium-high heat. Reduce heat to medium; cook, stirring occasionally, until brandy is reduced to 2 tablespoons, 7 to 8 minutes. Meanwhile, blend cherries in a blender or food processor until smooth.

Stir together brown sugar, ginger, allspice, and pepper in a shallow bowl. For sauce, add 3 tablespoons brown sugar mixture, the puréed cherries, and salt to brandy mixture in saucepan. Return to a boil; reduce heat to medium and simmer, stirring occasionally, until sugar is dissolved, about 3 minutes.

Remove vanilla bean from sauce; scrape out seeds. Stir seeds into sauce, then strain through a fine-mesh sieve. Return sauce to saucepan.

Whisk together water and cornstarch. Add to sauce. Bring to a boil over medium heat; reduce heat to medium-low. Cook, stirring constantly, until thickened, about 2 minutes. Remove from heat.

Dip cut sides of pears in remaining brown sugar mixture to coat evenly. Arrange pears, cut sides up, on prepared baking sheet. Brown sugared surface of pears with a kitchen torch, about 5 minutes for entire recipe. Serve pears with sauce. (Chill sauce in an airtight container up to 5 days.)