Strain cherries over a bowl, then reserve 80ml (⅓ cup) syrup. Add Chambord to the reserved liquid and set aside.
Use electric beaters to beat mascarpone, cream, icing sugar and vanilla in a bowl until thick soft peaks form. Fold in drained cherries.
Cut cake slices in half horizontally. Place half the cake slices in the base of a 6cm-deep, 18 x 28cm (base size) baking dish, trimming to fit as necessary. Drizzle the cake with half the cherry liquid mixture. Spread half the mascarpone mixture over the top to cover. Dust with cocoa. Repeat with another layer of cake, cherry liquid mixture and mascarpone mixture. Use a large palette knife or clean ruler to run across the top of the tiramisu to level, if desired. Cover and place in the fridge for 4 hours, or overnight, to chill.
Dust the tiramisu with cocoa just before serving.
