In a small bowl, sprinkle the gelatin over the cold water and let it sit for about 5 minutes to bloom.
In a medium saucepan, combine the heavy cream, whole milk, and granulated sugar.
Heat the mixture over medium heat, stirring occasionally, until the sugar is dissolved and the mixture is hot but not boiling.
Remove the saucepan from heat and add the bloomed gelatin to the hot cream mixture.
Stir until the gelatin is completely dissolved.
Stir in the vanilla extract.
Pour the mixture into ramekins or dessert cups.
Let them cool to room temperature, then cover with plastic wrap and refrigerate for at least 4 hours, or until set.
To unmold the Panna Cotta, dip the bottoms of the ramekins in hot water for a few seconds and then invert them onto serving plates.
Enjoy your meal!