Bloom the Gelatin: In a small bowl, sprinkle the gelatin powder over the cold water. Let it sit for about 5-10 minutes to soften. This is called "blooming" and it ensures the gelatin dissolves smoothly.

Infuse the Cream: In a medium saucepan, combine the heavy cream, milk, sugar, sliced ginger, and sliced lemongrass.

Heat the Mixture: Place the saucepan over medium heat. Bring the mixture to a simmer, stirring occasionally to dissolve the sugar. You'll see small bubbles forming around the edges. Don't let it boil!

Steep the Flavors: Once simmering, remove the saucepan from the heat. Cover it with a lid and let it steep for 30 minutes. This allows the ginger and lemongrass flavors to really infuse into the cream.

Add the Gelatin: After steeping, gently reheat the cream mixture over low heat until it's warm, but not simmering. Add the bloomed gelatin to the warm cream mixture. Stir constantly until the gelatin is completely dissolved. You shouldn't see any granules.

Strain the Mixture: Place a fine-mesh sieve over a large bowl or measuring cup. Carefully pour the cream mixture through the sieve to remove the ginger and lemongrass pieces. This will give you a smooth panna cotta.

Stir in Vanilla: Stir in the vanilla extract.

Pour into Serving Dishes: Divide the mixture evenly among small ramekins, glasses, or dessert cups.

Chill: Cover each dish with plastic wrap, making sure the plastic wrap touches the surface of the panna cotta to prevent a skin from forming. Refrigerate for at least 4 hours, or preferably overnight, until completely set. The panna cotta should be firm but still have a slight jiggle.