In a small bowl, sprinkle the agar-agar powder over the warm water.
Whisk to combine and let it stand for 5 minutes to bloom.
In a medium saucepan, combine the heavy cream, sugar, and vanilla extract.
Bring the mixture to a gentle boil over medium heat, stirring to dissolve the sugar.
Reduce the heat to low and simmer for 2-3 minutes.
Stir in the milk and the bloomed agar-agar mixture.
Continue to simmer for another 2-3 minutes, stirring constantly to ensure the agar-agar is fully dissolved.
Remove the saucepan from the heat. To cool the mixture quickly, you can place the saucepan in a larger bowl filled with ice water, stirring for about 15 minutes until it's lukewarm.
Carefully pour the mixture into five 4-ounce ramekins or custard cups.
Refrigerate for at least 4 hours, or preferably overnight, until fully set.
To serve, briefly dip the bottom of each ramekin in hot water. Run a thin knife around the edge to loosen, then invert onto a serving plate.
Garnish with fresh fruit or coulis and enjoy!
Don't let the mixture boil vigorously after adding the agar-agar, as this can weaken its setting power. A gentle, consistent simmer is all you need.