Step 1

Crust: Preheat oven to 350 degrees. In a food processor, pulse crackers with granulated sugar and salt until finely ground. (You should have about 1 1/2 cups.) Add butter; pulse until combined. Transfer to a 9-inch round tart pan with a removable bottom; firmly press into bottom and up sides. Place pan on a baking sheet and bake until crust is dry and set, 10 to 12 minutes. Transfer to a wire rack; let cool completely.

Step 2

Filling: Place cream cheese, sour cream, granulated sugar, egg, vanilla seeds, and salt in cleaned food processor; blend just until smooth. Fill crust with cheesecake mixture. Bake until filling is just set, 30 to 35 minutes. Transfer to a wire rack; let cool 1 hour. Refrigerate until cold, at least 2 hours and up to overnight.

Step 3

To serve, place 2 tablespoons superfine sugar in a sieve and evenly sift over top of cheesecake (avoiding crust). Move a small kitchen blowtorch back and forth across sugar until caramelized (aiming torch toward center to avoid burning crust). Repeat with remaining 2 tablespoons superfine sugar, making a second caramelized layer. Top with spun sugar and serve, slicing through spun sugar and cake with a sharp knife, and wiping blade between slices.