Melt the butter in a large cast-iron skillet over medium heat.
Add the sliced pears, dark brown sugar, ground cardamom, corn starch, vanilla extract, lemon juice, and salt to the melted butter in the cast-iron skillet, tossing to evenly combine.
Cook over medium heat, stirring, until the pears begin to soften, about 5-7 minutes.
Evenly sprinkle the clumpy crumble over the top of the pears and put the skillet in the pre-heated oven for 25-30 minutes, or until the pears are soft and the topping is golden brown. Don't worry if the topping looks moist when it first comes out of the oven, as it cools, it will crisp up!
Remove from the oven and let cool for 5 minutes before serving. Top with ice cream!