1. Prepare the Crust:

1. Toast black sesame seeds in a dry pan over medium heat until fragrant, about 3-5 minutes. Let cool, then grind into a fine powder in a spice grinder.
2. In a saucepan, combine heavy cream, milk, and sugar. Heat over medium until steaming but not boiling, stirring to dissolve sugar.
3. Sprinkle gelatin over cold water in a small bowl; let bloom for 5 minutes. Stir into warm cream mixture until fully dissolved.
4. Whisk in ground black sesame and vanilla extract. Strain through a fine-mesh sieve into a pitcher to remove any lumps.
5. Pour mixture into 4 ramekins or glasses. Chill in refrigerator for at least 4 hours or until set.
6. For mango coulis: blend mango, honey, lime juice, and salt until smooth. Strain if desired. Chill until ready to serve.
7. To serve, run a knife around edges of panna cotta and unmold onto plates, or serve in glasses. Top with mango coulis.