Muddle: Place the fresh watermelon cubes into the bottom of a cocktail shaker and muddle thoroughly to release all the juices.

Shake: Add the vodka, triple sec, and fresh lime juice to the shaker. Fill the shaker with ice.

Strain: Shake vigorously for 15 seconds until frost forms on the outside of the shaker. Double strain into a chilled martini or coupe glass to catch any watermelon pulp.

Garnish: Decorate the rim with a lime wheel or a small watermelon slice.