Heat the oven to 350°F (175°C). Wrap the outside of a 9-inch springform pan with 2–3 layers of heavy-duty foil to waterproof it; lightly grease the inside.
Make the crust: In a bowl, combine the graham cracker crumbs, 0.25 cup granulated sugar, and melted unsalted butter until evenly moistened and the mixture holds when pressed. Press firmly into the bottom and 1 inch up the sides of the pan. Bake until set and fragrant, 8–10 minutes. Cool 10 minutes. Reduce the oven to 325°F (165°C).
Start a kettle of hot water and place a large roasting pan on the middle oven rack to preheat for the water bath.
Make the filling: In a mixer on medium speed, beat the cream cheese until completely smooth, 2–3 minutes, scraping the bowl. Add 1 cup granulated sugar and the fine salt; beat until creamy and no graininess remains, 1–2 minutes. Mix in the sour cream and vanilla until blended, 30–60 seconds. Beat in the all-purpose flour just to incorporate. On low speed, add the eggs one at a time, mixing 20–30 seconds each just until combined; do not overmix.
Pour the filling over the crust and smooth the top. Set the foil-wrapped pan in the preheated roasting pan. Carefully pour about 2 quarts hot water into the roasting pan until it comes halfway up the sides of the springform.
Bake at 325°F until the edges are set and the center wobbles like gelatin in a 2-inch circle when gently shaken, 60–75 minutes.
Turn off the oven, crack the door, and let the cheesecake rest in the water bath for 1 hour to finish gently.
Remove the pan from the water bath, discard the foil, and run a thin knife around the edge to loosen. Cool on a rack until barely warm, about 1 hour, then refrigerate uncovered until fully chilled and set, at least 4 hours or overnight.
Release the springform ring. Slice with a thin knife dipped in hot water and wiped between cuts. Serve chilled.