Preheat your Yoder Smokers YS640s Pellet Grill to 500ºF, set up for direct grilling. When the grill comes up to temperature slide your GrillGrate grilling panels directly over the fire box.
Grill the watermelon with the door of the grill open to prevent the watermelon from completely breaking down. Flip when you have some nice grill marks and a little char. Repeat and remove from the grill.
Slice the red flesh away from the rind. Dice the flesh and place in the blender. Blend over low to medium-low speed so that flesh is pureed, but the seeds are not. Strain the liquid and discard the seeds.
To make the mint simple syrup, combine the Noble Saltworks Maple Smoked Turbinado Sugar, water and fresh mint in a Lodge 8” Cast Iron Skillet. Muddle the mint with a wood spoon and stip until the sugar is dissolved. Bring to a simmer and remove from heat. Place the mixture in a small blender cup or food processor and blitz to pulverize the mint leaves. You can choose to strain this or leaves the small flecks of mint in the syrup.
Combine the grilled watermelon juice, mint simple syrup, rum, lime juice and Jacobsen Salt Co. Kosher Salt and whisk to combine. Taste and adjust seasonings, as needed.
Pour the mixture into a large foil pan (or two smaller pans) and transfer to the freezer.
Let freeze for about 3 hours, then scrape and agitate with a fork. Return to the freezer and repeat the scraping again in another hour. Repeat this until the granita is light and flaky. At this point it can be stored in the freezer as is, and scraped again just before serving.
Garnish the watermelon mojito granita with fresh berries and a splash of rum, if desired.