Lightly grease the sides of a 9-inch springform pan and line the bottom with a parchment round. Pulse the cookies to fine crumbs, stir in the melted butter and salt, and press the mixture firmly into an even layer on the bottom only. Refrigerate at least 15 minutes.

Chop and melt the white chocolate until smooth. Cool until barely warm but still fluid, 5 to 10 minutes.

Beat the softened cream cheese on medium speed until completely smooth, about 2 minutes. Beat in the powdered sugar, vanilla, lemon juice, and salt, then stream in the cooled white chocolate and beat until silky.

If using gelatin, sprinkle it over the cold water and let it stand 5 minutes. Warm it gently just until dissolved (do not boil). Beat a spoonful of the cream cheese mixture into the gelatin, then beat that back into the bowl.

In a separate cold bowl, whip the cold heavy cream to medium-stiff peaks. Fold it into the cream cheese mixture in two additions until no white streaks remain.

Spread the filling over the chilled crust, smooth the top, cover, and refrigerate at least 8 hours, preferably overnight (about 12 hours).

For the topping, combine the cherries, sugar, lemon juice, and salt in a 2-quart saucepan. Cook over medium heat, stirring often, until the cherries simmer, 5 to 8 minutes (a little longer if frozen). Stir in the cornstarch slurry and cook 1 to 2 minutes more, until the juices are glossy and thick. Remove from the heat, stir in the vanilla or almond extract, and cool completely, then refrigerate until cold.

When the cheesecake is firm in the center, run a thin knife around the ring, unlatch, and lift the ring away. Spoon the cold cherry topping over the top. For clean slices, use a hot, dry knife, wiping the blade between cuts.