Preheat the oven to 350°F.
Toss the apple slices in lemon juice to keep them from browning. Add the sugar, cornstarch, and apple pie spice, then mix until the apples are evenly coated.
Roll out the crust and place it into the tart pan. Trim off any excess.
Arrange the apples inside the crust. Pour in any leftover liquid from the mixture.
Bake the apple tart for 45 minutes or until the filling is bubbly and the crust is golden.
Once baked, remove the tart from the oven and let it cool on a wire rack.
While the tart cools, prepare the caramel sauce. In a saucepan, combine sugar, water, and salt. Simmer over medium heat for about 5 minutes, stirring occasionally, until the sugar dissolves.
Once boiling, stop stirring to avoid scraping up any burnt bits from the bottom of the pan. Reduce the heat to medium-low.
Continue cooking the caramel sauce for 5 minutes, or until it turns a deep golden brown color.
Remove the saucepan from the heat. Stir in the heavy cream and butter until smooth.
Drizzle the salted caramel sauce over the cooled apple tart, and you're done. Enjoy!