Preheat your oven to 350°F.
Add the peeled and sliced apples to a large bowl. Add the melted butter, brown sugar, lemon juice, vanilla, cinnamon, nutmeg, cloves, allspice, salt and cornstarch. Toss until the apples are evenly coated.
Transfer the apple mixture and any juices in the bowl to a 9-inch cast-iron skillet. Spread into an even layer.
Combine the oats, flour, brown sugar, cinnamon and salt in a separate bowl. Add the cold cubed butter and work it into the dry ingredients with your fingertips, a fork or pastry cutter until coarse crumbs form.
Sprinkle the oat topping evenly over the apples.
Bake uncovered for 30–40 minutes, until the topping is golden brown, the filling is bubbling around the edges and the apples are tender when pierced with a knife.
Allow the apple crisp to cool for 10–15 minutes before serving. Serve warm with vanilla ice cream.