Prepare the Pie Crust
In a large bowl, whisk together flour, sugar, and salt. Add the cold, cubed butter and use a pastry cutter or your fingertips to work it into the flour mixture until it resembles coarse meal with some pea-sized pieces. Drizzle in ice water, 1 tablespoon at a time, mixing gently until the dough begins to come together. Form into a disk, wrap in plastic wrap, and refrigerate for at least 1 hour.Make the Salted Caramel
In a medium, heavy-bottomed saucepan, heat sugar over medium heat, stirring constantly with a high heat-resistant spatula or wooden spoon. The sugar will form clumps and eventually melt into a thick brown liquid as you continue to stir. Once sugar is completely melted, immediately add butter. The caramel will bubble rapidly – this is normal! Stir butter into caramel until completely melted, about 2 minutes. Very slowly drizzle in heavy cream while stirring. The mixture will bubble aggressively again. Allow to boil for 1 minute, then remove from heat and stir in sea salt. Let cool slightly.Roll Out the Pie Crust
Preheat your oven to 375°F (190°C). Remove dough from refrigerator and let sit at room temperature for 10 minutes to soften slightly. On a lightly floured surface, roll the dough into a 12-inch circle. Transfer to a 9-inch pie dish, trim excess, and crimp edges. Refrigerate while preparing filling.Prepare the Pumpkin Filling
In a large bowl, whisk together pumpkin puree and eggs until well combined. Add brown sugar, spices, and salt, whisking until incorporated. Gradually stir in heavy cream and milk. Finally, fold in 1/3 cup of the cooled salted caramel (reserve the rest for topping).Assemble and Bake the Pie
Pour the pumpkin-caramel mixture into the chilled pie crust. Tap the pie dish gently on the counter to remove any air bubbles. Cover the edges of the pie crust with aluminum foil or a pie shield to prevent over-browning. Bake for 55-60 minutes, or until the center is almost set but still slightly wobbly (it will firm up as it cools). A knife inserted about 1 inch from the edge should come out clean.Cool and Garnish
Allow the pie to cool completely on a wire rack for at least 3 hours (ideally 4-6 hours for cleaner slices). Before serving, warm the remaining salted caramel sauce slightly and drizzle over the pie. Add a sprinkle of flaky sea salt and serve with whipped cream if desired.