In a small bowl, sprinkle the unflavored gelatin over the cold water and let it bloom for 5-10 minutes.
In a medium saucepan, combine the heavy cream and granulated sugar. Heat over medium heat, stirring occasionally, until the sugar is dissolved and the cream is warm (do not boil).
Remove the saucepan from the heat. Stir in the bloomed gelatin mixture until it is completely dissolved. Add the vanilla extract and stir to combine.
Pour the mixture into individual ramekins or a larger mold. Cover and refrigerate for at least 4 hours, or until firm.
To serve, you can unmold the panna cotta onto plates or serve it directly from the ramekins. Garnish as desired.
Notes
Optional garnishes include fresh berries, a raspberry sauce, or a caramel drizzle.