Preheat oven to 140ºC fan bake or 160ºC regular bake. Grease 3 x 20cm round cake tins and line with baking paper.
Prepare cake batter according to instructions on the box. Divide evenly between prepared tins and bake for 15-20 minutes, until a skewer inserted into the centres, comes out clean. Leave to cool in tins for 10 minutes, before turning out onto a wire rack to cool completely.
Meanwhile, pit and halve approximately three-quarters of the cherries. Make the icing according to instructions on the box. Whip the cream to medium peaks.
Place one of the cake layers on a serving plate or stand. Spread with half of the jam, then gently spread half of the cream over the top. Add half of the pitted cherries. Place another cake layer on top and repeat.
Add the final cake layer. Spread icing on top. Garnish with the remaining whole cherries. Sprinkle dark chocolate over the top.
As this cake contains fresh cream and cherries, it will need to be served soon after assembling, or refrigerate until required.