a 9-inch fluted tart pan with a removable bottom; kitchen torch
For the crust: Position a rack in the center of the oven and preheat the oven to 375 degrees F.
Place the graham crackers, sugar and salt in the bowl of a food processor. Process until the crumbs are very fine, about 1 minute. Dump the crumbs into a medium bowl, then dust out the bowl of the food processor with a paper towel, and place the bowl and blade back on the machine.
In a small heatproof bowl, combine the butter, 2 teaspoons water and the vanilla extract. Heat in the microwave on high power until the butter melts, about 45 seconds. Stir to blend, and then pour into the crumbs. Use a fork to toss the mixture until its evenly moistened; when you grab a fistful of crumbs and squeeze, it should hold together like damp sand (if not, add a bit more water, 1/2 teaspoon at a time, until you get there). Turn the crust mixture into the tart pan, and pat into the bottom and up the sides of the pan. Use a flat-bottomed measuring cup to press the crust firmly into place. Bake until lightly golden, fragrant and firm, about 8 minutes. Cool on a wire rack while you prepare the filling.
For the filling: Reduce the oven temperature to 300 degrees F. In the bowl of the food processor, grind 6 tablespoons of the sugar until noticeably finer, about 1 minute (you'll notice a bit of sweet smoke rising up into the air from the processor-this is the sign that the sugar is breaking down). Add the yogurt, vanilla extract, orange zest, salt, eggs and cream cheese. Blend until perfectly smooth. Pour the filling into the prepared crust.
Bake until the filling is set at the edges but still quite wobbly towards the center, about 30 minutes.
Cool the tart on a wire rack for about 15 minutes. Transfer to the refrigerator and chill uncovered until very firm, at least 4 hours or up to overnight.
Remove the ring from the tart pan and place the tart on a heatproof serving platter. Sprinkle the remaining 3 tablespoons sugar over the surface of the tart and smooth it out evenly, covering the entire surface. Use a kitchen torch to melt and caramelize the sugar, scorching a bit in spots. Let the sugar harden for a few minutes, then cut and serve.