Preheat oven to 350˚F.
Crust: Place cereal into a food processor and pulse until roughly crumbled. Remove 1 cup and add 2 tablespoons butter to the reserved cup and toss together. Set aside.
With the motor running, finely crush remaining cereal, while adding remaining butter, until fully incorporated.
Pour mixture into the bottom of an 8”x 8” tart shell and press into the bottom and sides. Refrigerate for at least 30 minutes and up to 1 day.
Filling: Place apples into a large mixing bowl and add remaining ingredients. Gently but thoroughly toss together until well mixed.
To assemble: Drizzle 1/2 cup salted caramel sauce evenly into the bottom of the prepared tart shell.
Top caramel sauce with apples, evenly arranged, filling the entire tart shell.
Drizzle another 1/4 cup caramel sauce over apples and dot with butter. Place tart onto a baking sheet and bake in oven for 25 to 30 minutes or until pie is bubbling.
Remove from oven and sprinkle reserved cereal crumble on top.
Place tart back into the oven and bake for an additional 15 to 20 minutes.
Remove tart from oven and cool, about 30 minutes.
Drizzle remaining caramel sauce over tart, sprinkle with sea salt flakes and serve.