Preheat oven to 350 degrees.

First, you'll need to prepare your caramel sauce. In a medium-sized heavy bottomed pot, heat water and sugar on HIGH heat and whisk just until the sugar is dissolved. It is extremely important that you have your stove on high heat or you run the risk of seizing up the sugar, turning it into a solid mess. Once sugar is dissolved, put the whisk to the side and start swirling the pot by the handle in circular motions. It's very important that you don't disturb the caramelization process too much and is why you'll need to swirl instead of whisk. Swirl constantly until the melted sugar turns a dark amber color, this will take about 5 minutes or so. The darker the amber color, the more intense caramel flavor you will have. After it turns dark amber, slowly and carefully pour in heavy cream. It will bubble up violently so you will need your whisk to whisk it very fast until it comes back down and it will start looking like caramel at this point. Remove from heat and stir in butter and vanilla. Allow to cool down slightly.

In a large bowl, prepare your crumble topping by whisking the flour, brown sugar, granulated sugar and salt together. Cut in the butter using your hands or a fork until mixture is crumbly but will still mold together when you squeeze it. Set aside.

In a large cast-iron skillet, melt butter on medium-low heat and stir in sliced apples and salt. Cook apples, stirring often until tender, 5-7 minutes. If apples released a lot of liquid, drain or blot with a paper towel. Stir ¾ of the prepared caramel sauce in with the apples and sprinkle the crumble topping on top. Place skillet in the oven and bake for 20-25 minutes or until the topping turns lightly golden brown and the caramel bubbles on the sides. Drizzle remaining caramel on top and serve with vanilla ice cream, if desired.

Caramel apple crisp will keep for up to 3 days stored in an airtight container or covered with plastic wrap at room temperature.