Combine cherries, sugar and kirsch in a small saucepan. Cook over medium heat for 4 to 5 minutes until cherries soften and release their juice.

Stir cornstarch into the cold water, add to the pan, and simmer 1 to 2 minutes until glossy and thick enough to coat the back of a spoon. Remove from heat and cool to room temperature.

Melt chopped chocolate with 120 ml of the cream in the microwave in 20-second bursts, stirring between each, about 1 to 2 minutes total until smooth. Cool the ganache to room temperature, around 68 F/20 C.

Whip the remaining 360 ml cream with sugar, vanilla and salt to soft-medium peaks, when the beaters lift and leave a peak that droops slightly at the tip.

Fold the cooled ganache into the whipped cream in 3 additions, folding gently each time until no streaks remain and the mousse holds its shape on a spoon.

Divide the cooled cherry compote among 6 glass cups or jars, about 2 tablespoons each.

Spoon or pipe mousse over the compote, filling cups about three-quarters full. Tap cups gently on the counter to settle any air pockets.

Chill uncovered for 2 hours, or cover and chill up to 24 hours, until the mousse is set enough to hold a spoon mark.

Before serving, top each cup with whipped cream, chocolate shavings and a fresh cherry. Dust with cocoa powder if using.