1. In a small bowl, sprinkle gelatin over cold water and let it bloom for 5 minutes.
2. In a saucepan, combine heavy cream, milk, sugar, and lemongrass. Heat over medium heat until it just starts to simmer. Remove from heat and let it steep for 10 minutes.
3. Strain the mixture to remove lemongrass pieces. Return the mixture to the saucepan and reheat gently.
4. Add the bloomed gelatin to the warm mixture and stir until completely dissolved.
5. Pour the mixture into serving glasses and refrigerate for at least 4 hours or until set.