For the granizado:
Combine the mango and passion fruit pulp in the jar of the blender with one cup of water and process until smooth and well combined. Stir in the simple syrup a little at a time until sweetened to taste. Please note that it will lose some of its sweetness when completely frozen. Cover with aluminum foil and set in the coldest part of your freezer for about one hour. Using a fork, scrape the ice crystals that have formed into the center of the pan, mashing and blending as you go. Cover and return to the freezer. Repeat every 30 minutes or so until the mixture is uniformly frozen about 2 to 3 hours depending on your freezer. Serve immediately or cover tightly and freeze overnight. If serving the next day, use a fork to scrape off the ice crystals and scoop into dessert glasses. Garnish with mint and serve.
As an alternative, frozen fruit pulps are widely available in large chain grocery stores and Latin American markets in a variety of tropical flavors. Unsweetened with no additives, they're a great way to try new flavor combinations with produce that might typically be out of reach.
For the simple syrup:
For this recipe, it's better to make more than you need so the sweetness can be adjusted to the ripeness of the fruit. Leftover syrup can be covered and refrigerated for up to one month.
Combine sugar and water in a small saucepan over medium heat. Stir until the sugar is completely dissolved, about 5 minutes. Set aside and cool to room temperature. Cover and refrigerate until ready to use.