In a small bowl, combine cold water with unflavored powdered gelatin and let it sit for 5 to 10 minutes.

In a medium saucepan, mix heavy cream, whole milk, strong brewed coffee, granulated sugar, and pure vanilla extract. Heat and stir until just boiling, about 5 minutes.

Remove from heat and stir in the softened gelatin until fully dissolved. Return to low heat if necessary.

Pour the mixture into individual serving dishes, cover with plastic wrap, and refrigerate for at least 4 hours.

For optional syrup, heat additional brewed coffee with granulated sugar until dissolved. Chill before serving.

Serve the panna cotta drizzled with syrup and optional garnishes like whipped cream.