In a medium bowl stir together the pears and bourbon. Let stand ’till tender for 20-30 minutes, depending on the firmness of the pears.
While you wait, stir together the sugars, flour, and cinnamon in another bowl. Add to the pear mixture and stir to coat evenly.
Generously butter a 10-inch cast-iron frying pan. Dust with a bit of flour to minimize sticking. Add the pear filling to the prepared pan.
Preheat an oven to 375°F (190°C).
For the topping, in a bowl, stir together the melted butter and vanilla. In a larger bowl stir together the flour, oats, brown sugar, and salt with a fork. Add the butter mixture to the larger bowl and stir until evenly blended and crumbly.
Spread over the pears.
Bake until the pears are tender and the topping is crispy, golden, and brown (30-35 minutes).
Allow to cool slightly and serve with vanilla ice cream.