1. Prepare the Watermelon Bowls:

• First, create stable bases for your watermelon bowls. Trim a very thin slice from the stem end and the opposite end of each whole watermelon. This allows the finished halves to sit flat and level without tipping over.
• Cut each watermelon in half crosswise. You should now have four watermelon “bowls.”
• Using a large spoon, carefully hollow out each watermelon half, leaving about a ½-inch-thick shell of pink flesh attached to the rind. Be careful not to break through the bottom of the shell.
• Reserve all the watermelon flesh you scoop out.
• Place the four empty watermelon halves, cut-side up, on a rimmed baking sheet. This will help you carry them and keep them level in the freezer.

2. Make the Watermelon-Lime Juice Base:

• Working in batches if necessary, place the reserved watermelon flesh into a blender and blend until it becomes a smooth juice.
• Measure out exactly 8 cups of the fresh watermelon juice and place it in a large mixing bowl. (You can save any remaining juice for drinking – it’s delicious!).
• Add the ½ cup of granulated sugar and the ¼ cup of fresh lime juice to the bowl with the watermelon juice. Whisk thoroughly until all the sugar is completely dissolved.

3. Freeze the Granita Base:

• Pour this watermelon-lime juice mixture evenly among the four hollowed-out watermelon halves on your baking sheet.
• Carefully place the baking sheet with the filled watermelon halves into the freezer. Make sure they are sitting flat and level.
• Freeze until the juice is completely solid, which will take about 8 hours, or preferably overnight.

4. Prepare and Chill the Margarita Topping:

• While the watermelon freezes (or at any point before serving), prepare the alcoholic topping.
• In a small airtight container or jar, mix the ½ cup of tequila blanco and the ¼ cup of triple sec together.
• Seal the container and place it in the refrigerator (or freezer – it won’t freeze solid) to get it very cold.

5. Scrape and Serve the Granita:

• When you are ready to serve, remove the baking sheet with the frozen watermelon bowls from the freezer.
• Working with one bowl at a time, take a sturdy fork and use the tines to scrape the surface of the frozen watermelon juice. Scrape back and forth to create light, fluffy ice crystals – a granita! Be careful not to scrape so hard that you break through the watermelon shell.
• Drizzle about 3 tablespoons (1.5 ounces) of the chilled tequila-triple sec mixture over the fluffy ice in each bowl.
• Garnish each Watermelon Margarita Granita with a fresh lime wheel and a festive cocktail umbrella, if using.
• Serve immediately with spoons. As the recipe notes, as the granita begins to melt, you can replace the spoons with straws and enjoy the rest as an icy-cold watermelon margarita!