Preheat the oven to 375 degrees F. Line a baking sheet with parchment.
For the bourbon pears: Mix the bourbon and vanilla extract in a medium bowl and add the pear slices, tossing gently to coat. Set aside to soak for about 20 minutes while you prepare the topping and crust.
For the topping: Combine the brown sugar, butter and flour into small lumps and set aside.
For the crust: Roll out the puff pastry sheet on a lightly floured surface into a 14-inch square. Transfer to the prepared baking sheet (it's ok if the dough hangs over the edges).
Drain the pears (save the bourbon mixture for a cocktail!) and toss with the granulated sugar. Arrange the pear slices overlapping in rows on the dough, leaving a 2-inch border around the whole tart. Fold and pleat the edges of the dough over, so it just overlaps the pears. Brush the puff pastry with the melted butter and sprinkle the topping over the pears.
Bake until the pastry is a golden brown, 40 to 45 minutes. We're drooling while writing this so you must be too!