Preheat oven to 350 degrees F. Grease a 10-inch cast iron skillet and set aside.
In a large mixing bowl, combine pears, lemon juice, and vanilla. Toss to coat the pears. In a medium bowl mix together sugars, flour, cornstarch, cinnamon, and nutmeg. Sprinkle sugar mixture over pears and stir until combined. Pour pear mixture into prepared skillet and spread into an even layer. Set aside.
In a small saucepan, melt 1/2 cup of the butter over medium-low heat and continue to cook, swirling occasionally, until butter turns golden brown, Skim foam from top, and remove from heat. Pour into a bowl to stop the cooking, leaving any burned sediment behind; let cool.
In a large bowl, combine the oats, flour, salt, cinnamon, and brown sugar. Pour the browned butter over the mixture and stir well. Add in the remaining 2 tablespoons of cold butter and mix until crumbly. Pour mixture evenly over the pears.
Bake for 40-45 minutes or until the crumble topping it golden brown and the crisp is bubbling around the edges. Let cool for 10 minutes before serving. Serve warm with vanilla ice cream, salted caramel sauce, or whipped cream, if desired.
Note-if you don't have a cast iron skillet you can bake the crisp in a greased baking dish.