1. Preheat oven to 425 degrees with rack in center. Generously butter inside and rims of four 6-ounce ramekins. Sprinkle with granulated sugar to coat insides of ramekins, shaking out the excess. Place ramekins on a rimmed baking sheet and refrigerate until needed.

2. Bring milk to a simmer in a medium saucepan over medium. Whisk together cornstarch and 1/3 of the passion fruit puree in a medium bowl until smooth. While continuing to whisk, slowly pour half the hot milk over passion fruit mixture; whisk until incorporated. Return passion fruit mixture to saucepan, and cook, whisking constantly, over medium until mixture thickens, 1 to 2 minutes. Remove pan from heat, and whisk in remaining passion fruit puree. Cover to keep warm, and set aside.

3. Place egg whites and lemon juice in the bowl of an electric mixer fitted with the whisk attachment; beat on medium-low speed just until foamy. Increase speed to medium-high, and add granulated sugar, beating until soft peaks form. Add 1/3 of the egg white mixture to reserved passion fruit mixture, and whisk until just combined. Using a rubber spatula, gently fold in remaining egg white mixture until just incorporated.

4. Evenly divide passion fruit mixture among prepared ramekins, gently smoothing tops with the back of a spoon. Bake until puffed and lightly golden, 14 to 16 minutes. The surface of the souffles should be firm with centers that are slightly runny. Carefully remove baking sheet from oven. Dust tops with confectioners' sugar. Scoop a scant teaspoon from center of each souffle, and fill with passion fruit seeds and pulp. Serve immediately.