01 - Set oven to 350°F (175°C) and allow to fully preheat.
02 - In a large bowl, combine sliced apples, granulated sugar, flour, cinnamon, nutmeg, and salt. Toss until apples are evenly coated.
03 - Spread apple mixture evenly into the base of a 9-inch square baking dish.
04 - Heat granulated sugar in a small saucepan over medium heat, stirring with a wooden spoon until sugar melts and turns deep amber. Add butter and whisk until fully incorporated. Slowly pour in heavy cream, whisking continuously, until sauce is smooth. Stir in flaky sea salt. Remove from heat.
05 - Pour warm salted caramel sauce evenly over the apple filling.
06 - In a medium bowl, stir together oats, flour, brown sugar, cinnamon, and salt. Add cubed butter and mix with fingers or a pastry cutter until mixture forms large, moist crumbs.
07 - Distribute oat topping evenly over the apples and caramel. Bake for 35 to 40 minutes, until topping is golden and filling bubbles along edges.
08 - Allow apple crisp to cool for 15 minutes before serving. Portion while warm.