Remove the seeds from a ripe watermelon and cut it into chunks.

Blend the chunks until smooth, then strain the juice through a fine mesh to remove any pulp.

Fill a cocktail shaker with ice cubes.

Add the vodka, freshly squeezed watermelon juice, triple sec, and lime juice to the shaker.

Shake well until the outside of the shaker feels cold.

Strain the mixture into a chilled martini glass.

Garnish with a small slice of watermelon or a lime wheel on the rim of the glass.

Serve immediately and enjoy the fresh, fruity flavors of your Watermelon Cosmopolitan.