For the panna cotta: Place the sugar, coconut milk, cream and vanilla pod in a small saucepan over medium heat. Heat, stirring gently, until the sugar dissolves, 2 to 3 minutes. Bring to a simmer, then remove from the heat and stir in the coconut essence. Set aside.
Remove the vanilla pod with a slotted spoon, and discard. Gently wring out any excess water from the gelatin; add the gelatin to the cream mixture, stirring until dissolved.
Divide the mixture between 4 ramekins. Chill for 2 to 3 hours, until set.
Meanwhile make the syrup: In a small saucepan, simmer together the ginger, lime juice, sugar and 1/4 cup water until it has reduced and thickened slightly, 15 minutes. Strain and set aside.
Serve the panna cotta with a drizzle of syrup.
For a firmer set, or if you want to unmold the panna cottas, use four gelatine leaves instead of three.