Begin by placing the cubed watermelon in a blender. Blend until smooth to create a vibrant watermelon puree. If you prefer a smoother texture, you can strain the puree through a fine mesh sieve to remove any pulp.
In a large glass or cocktail shaker, add the fresh mint leaves and sugar (or simple syrup). Use a muddler or the back of a spoon to gently muddle the mint leaves. This will release the essential oils and aroma, infusing the drink with its refreshing flavor.
Add the watermelon puree, fresh lime juice, and white rum to the muddled mint. Stir well to combine all the ingredients. This captivating blend of watermelon, mint, and lime forms the heart of your mojito.
Fill two glasses with ice cubes. Divide the watermelon mojito mix evenly between the glasses. Top up each glass with a splash of club soda or sparkling water, giving the drink a delightful fizz.
Garnish each glass with a sprig of fresh mint and a small wedge of watermelon or lime for an extra pop of color. Serve immediately and enjoy the invigorating taste of summer!