If you haven't already, make the pie dough. Make the caramel. Combine 1½ cups (250g) sugar and 6 Tbsp (90ml) water in a saucepan over medium-high heat. Cook undisturbed until the sugar has turned a deep amber hue, about 12-15 minutes. Tip: don't get caught up on the time, just watch the caramel based on temperature and color.
Finish the caramel. Carefully and slowly drizzle in 1 cup (237ml) heavy cream while whisking, then cook until caramel is smooth and the cream has fully incorporated. Remove the pan from the heat, then add 1¼ tsp Kosher salt and 4 Tbsp (57g) butter. Whisk until combined, then set aside.
Make the apple pie filling. Combine 2 tsp lemon juice and 6 cups apples in a large bowl. Add 2 Tbsp (16g) flour, 2 tsp (5g) cinnamon, and 2 Tbsp (15g) sugar, then toss to combine.
Make the egg wash. Preheat oven to 375°F (190°C). Whisk together 1 large egg with 2 tsp water, then set aside.
Prepare the pie dough. Roll out one round of dough on a lightly floured surface to a 12"x17" rectangle. Transfer through onto a 15" x 10" x 1" jelly roll pan. Gently press the dough into the edge of the pan and trim off excess dough, leaving a ¾" overhang around all edges. Use any excess dough to fill in spots where the dough cracked or wasn't long enough.
Add the filling. Pour prepared apples into the pan and spread out to fill evenly. Drizzle the caramel evenly over the filling. Note: If it's hard to pour, reheat the caramel slightly beforehand.
Roll out the 2nd pie dough: Roll out your remaining piece of dough into a 12" x 17" rectangle. Either roll dough onto your rolling pin and transfer to the pie OR cut into strips to create lattice top. Fold the bottom edge over the top, crimping with your fingers as desired. If you did not make a lattice pattern, use a knife to vent the pie. Brush the egg wash on top.
Bake the apple pie. Bake in a preheated oven for 50-60 minutes, or until the top is golden brown and the caramel inside is bubbling. Rotate pie halfway through cooking. Allow the pie to cool for at least 1 hour, then serve with homemade cinnamon whipped cream or ice cream!
Make the whipped cream. While the pie is cooling, pour 1 cup (236ml) heavy cream into the bowl of a stand mixer. Beat on high speed until soft peaks begin to form. Stop the mixer and add 1 tsp (4g) vanilla extract, 3 Tbsp (23g) powdered sugar, and 2 tsp (5g) cinnamon. Continue to mix until stiff peaks form, then serve immediately with pie.