Prep Pan & Oven: Preheat oven to 325°F (163°C). Generously grease a 9-inch springform pan and line the bottom with a circle of parchment paper. Wrap the outside bottom and sides of the pan tightly with 2 layers of heavy-duty aluminum foil to protect against water leakage.

Bake the Graham Crust: In a medium bowl, combine graham cracker crumbs, melted butter, 2 tablespoons brown sugar, and 1/2 teaspoon cinnamon until evenly moistened like wet sand. Press firmly into the bottom and slightly up the sides of the prepared springform pan. Bake at 325°F for 10 minutes, then remove and cool while preparing the filling.

Whip Cheesecake Filling: In a large mixing bowl or stand mixer fitted with the paddle attachment, beat softened cream cheese and granulated sugar on low speed for 2 to 3 minutes until silky smooth and lump-free. Add sour cream and vanilla extract, mixing just until combined. Add eggs one at a time, mixing on low speed after each addition just until incorporated (do not over-whip, which incorporates excess air).

Water Bath Bake: Pour the smooth cheesecake batter over the cooled crust. Place the foil-wrapped springform pan inside a large roasting pan. Pour boiling hot water into the roasting pan until it reaches halfway up the sides of the springform pan. Bake at 325°F (163°C) for 55 to 65 minutes until the edges are set and lightly golden, but the center 2-inch circle still jiggles slightly like set gelatin.

Gradual Oven Cooling: Turn off the oven, crack the oven door open about 1 inch with a wooden spoon, and leave the cheesecake inside for 1 hour to cool gradually without thermal shock (this prevents cracking!). Remove from water bath, discard foil, and chill in the refrigerator for at least 4 hours or overnight.

Cook Caramel Pecan Topping: In a medium heavy-bottomed saucepan over medium heat, melt 1/2 cup butter and 1 cup dark brown sugar together, stirring until dissolved. Stir in 1/2 cup heavy cream, cinnamon, and nutmeg. Bring to a gentle rolling boil for 3 to 4 minutes until thickened into a glossy amber caramel sauce. Remove from heat and stir in toasted chopped pecans. Cool for 15 minutes until warm and pourable.

Assemble & Slice: Run a thin knife around the rim of the springform pan and remove the outer collar. Pour the warm caramel pecan pie topping generously over the chilled cheesecake, letting it cascade slightly down the sides. Sprinkle with flaky sea salt. Slice with a warm knife and serve immediately!