Heat the oven to 325°F (163°C) with a rack in the center. Butter an 8-inch round pan about 2 inches deep and line it with parchment. Have a larger pan ready for a water bath.

Bring the water and sugar to a boil in a saucepan. Add the butter and let it melt. Remove from the heat, add the chopped chocolate and let it soften for a few minutes.

In a separate bowl, whisk the eggs with the rum.

Whisk the chocolate mixture until smooth, then gently whisk it into the egg mixture.

Pour the batter into the prepared pan, set it inside the larger pan and add about an inch of warm water to the outer pan.

Bake for about 1 hour, until set but still slightly soft in the center. Cool on a wire rack.

Bring the raspberries and sugar to a boil in a heavy saucepan, then simmer for about 3 minutes.

Whisk in the cornstarch slurry until the sauce thickens slightly.

Puree in a food processor, then strain through a fine sieve to remove the seeds. Pour into a squeeze bottle, thinning with a splash of water if needed.

Whip the cream to stiff peaks, then gently fold in the vanilla and powdered sugar.

Cut the cake into hearts with a heart-shaped cutter. Drizzle raspberry sauce on each plate, set a cake heart on top and add whipped cream.

Garnish with fresh raspberries, a mint sprig and grated dark chocolate.