Make the Panna Cotta
In a medium saucepan, combine the heavy cream, milk, sugar, vanilla bean (pod and seeds), and cardamom.
Heat over medium heat, stirring occasionally, until the mixture is hot and just beginning to steam. Do not let it boil.
While the cream mixture heats, sprinkle the gelatin over the cold water in a small bowl. Let it bloom for about 5 minutes.
Remove the cream mixture from the heat. Add the bloomed gelatin and stir until fully dissolved.
Stir in the blood orange zest and juice.
Strain the mixture through a fine-mesh sieve to remove zest and spices for an ultra-smooth texture.
Divide the panna cotta evenly between serving glasses or ramekins. Let cool slightly, then cover and refrigerate for at least 4 hours, or until fully set.
Make the Blood Orange Coulis (Optional)
In a small saucepan, combine blood orange juice and sugar. Heat gently, stirring until the sugar dissolves.
For a thicker coulis, whisk the cornstarch with a tablespoon of cold water and stir it into the juice. Simmer briefly until slightly thickened.
Cool completely, then refrigerate until ready to use.
To Serve
Spoon the cooled blood orange coulis over the set panna cotta.
Garnish with extra zest or fresh blood orange segments if desired.
Disclaimer: I am not a certified nutritionist. Nutrition facts are calculated using an automated database of common ingredients and are intended as an estimate only. Variations can occur depending on product brands, measuring methods, and ingredient swaps.