Keep molds ready.
In a thick bottom pan, combine heavy cream, milk, and sugar, bring the mixture to a boil. This takes about 5 mins.
Lower the heat and add the agar powder. Whisk vigorously until it completely dissolves; simmer for 2 - 3 minutes.
Microwave the chocolates for 30 secs - 1 min to melt.
Remove from heat and then stir in melted chocolate. Whisk well to combine the chocolate into the milk.
Next, add the vanilla and mix again.
Pour the mixture into the selected molds / bowls. Cool a little bit, then refrigerate for at least 3 - 4 hours.
When ready to serve, dip the mold in hot water and run a sharp paring knife around the edges and then invert onto the serving plate.
Dust with cocoa powder and sprinkle the hearts for decoration, serve.
Alternatively, you can serve with whipped cream, ice cream, and grated chocolate.