Fill a tall glass to the rim with pebble ice.

Pour the watermelon syrup over the ice and let it pool before the ginger ale goes in.

Tilt the glass and pour the ginger ale slowly down the inside wall, stopping when the fizz climbs near the rim and settles back down.

Pour the half-and-half over the back of a spoon so it clouds the pink soda into soft streaks.

Stir once, tuck the watermelon wedge and mint sprig against the rim, and serve immediately while the mint is still fragrant.