Pour the cold water into a small bowl. Sprinkle the gelatin evenly over the water and let it bloom for 5 minutes.
In a medium saucepan, combine the heavy cream and sugar. Scrape the seeds from the vanilla bean pod into the cream mixture. Add the scraped pod to the pan as well.
Heat the cream mixture over medium heat, stirring occasionally, until the sugar dissolves and the mixture just begins to steam around the edges. Do not let it boil.
Remove the saucepan from the heat. Remove and discard the vanilla bean pod.
Add the bloomed gelatin mixture to the warm cream. Whisk gently until the gelatin is completely dissolved and no granules remain.
Pour the mixture through a fine-mesh sieve into a clean bowl to catch any undissolved bits or impurities, ensuring a smooth result.
Carefully pour the liquid into individual ramekins or serving glasses.
Cover each serving dish with plastic wrap, touching the surface of the liquid to prevent a skin from forming.
Refrigerate for at least 4 hours, or until completely set and firm to the touch.
Notes
For the smoothest texture, make sure the gelatin is fully dissolved before chilling.
Chilling time is crucial; do not rush this step if you want a perfect wobble.
To unmold the panna cotta, briefly dip the bottom of the ramekin in hot water before inverting onto a plate.