Heat the oven to 325°F (165°C). Wrap the outside of a 9-inch springform pan in two layers of heavy-duty foil so no water can seep in.
Make the crust: stir the graham cracker crumbs, sugar, melted butter, and salt together until the crumbs look like wet sand. Press firmly into the bottom of the pan and about 1 inch up the sides. Bake for 10 minutes, then set aside to cool. Keep the oven on.
Beat the filling: in a large bowl, beat the cream cheese on medium speed until completely smooth, about 2 minutes, scraping the bowl down twice. Beat in the sugar, then add the eggs one at a time, mixing just until each disappears. Beat in the sour cream, vanilla, flour, and salt on low speed until just combined — do not overmix.
Pour the filling over the cooled crust and smooth the top. Tap the pan gently on the counter a few times to pop any air bubbles.
Bake in a water bath: set the foil-wrapped pan inside a larger roasting pan and pour hot water into the roasting pan until it comes halfway up the sides of the springform. Bake for 60–70 minutes, until the edges are set and the center still jiggles slightly when you nudge the pan.
Cool slowly: turn the oven off, crack the door open, and leave the cheesecake inside for 1 hour. Remove from the water bath, run a thin knife around the edge, and cool to room temperature, about 1 hour more. Cover and refrigerate for at least 4 hours, or overnight.
Make the pecan topping: in a medium saucepan over medium heat, melt the butter with the brown sugar, maple syrup, and heavy cream, stirring until the sugar dissolves and the mixture bubbles, about 2–3 minutes. Stir in the pecan halves, vanilla, and salt. Simmer for 1 minute, then remove from the heat and cool for 10 minutes so it thickens slightly.
Spoon the warm topping over the chilled cheesecake, spreading the pecans into an even layer and letting the caramel drip down the sides. Chill for 30 minutes to set the topping, then slice with a hot, dry knife, wiping the blade between cuts.