Let's cook.
In a small bowl, sprinkle the gelatin powder over the cold water. Let it sit for 5 minutes to bloom and soften.
In a medium saucepan, combine the heavy cream and granulated sugar. Heat over medium-low heat, stirring occasionally, until the sugar is fully dissolved and the cream is warm but not boiling, about 3-5 minutes.
Remove the saucepan from the heat. Add the bloomed gelatin mixture to the warm cream, stirring constantly until the gelatin is completely dissolved.
Stir in the cooled strong brewed espresso and vanilla extract until well combined.
Divide the panna cotta mixture evenly among four 4-ounce ramekins or small serving glasses.
Refrigerate for at least 4 hours, or preferably overnight, until the panna cotta is set and firm.
To serve, you can dip the bottom of each ramekin briefly in warm water to help loosen, then invert onto a serving plate. Garnish with chocolate shavings or a dusting of cocoa powder, if desired.
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