In a high-speed blender, combine chilled, chopped watermelon with ice cubes, fresh mint leaves, spices, lime juice, chopped ginger, and jalapeño slices (if using). Sprinkle in some black salt for flavor. You may add a bit of sugar for sweetness, though I skip it.
Blend on high until the mixture becomes smooth and velvety, with no chunks remaining. There's no need to add water, as the watermelon releases enough natural juice to create a perfectly pourable consistency.
For the glass rim, mix chaat masala and red chili powder on a small plate. Run a lime wedge around the rim of each serving glass to moisten it, then dip the edge into the spice mix and gently rotate to coat evenly.
Add a few ice cubes to each glass, pour in the chilled watermelon jaljeera, and garnish with a fresh mint leaf. Serve immediately and enjoy this tangy, spicy, and cooling summer drink!
Notes
Avoid adding too much ice while blending, as it can dilute the flavors. For the best taste and texture, make sure your watermelon is thoroughly chilled before blending.
The watermelon jaljeera can be stored in the refrigerator for up to a day, though it's best enjoyed fresh on the same day.
Naturally, it may separate a bit as it sits; simply stir it well with a spoon before serving to bring everything back together.
For an extra punch, try adding a tiny pinch of coarse salt to the rim spice mix. It adds a subtle depth of flavor, but use it sparingly to avoid overpowering the drink.