Take the chocolate mousse quenelle out of the blister. Put on a plate or tray and cover with plastic and defrost in the fridge.
Mix the water together with the cherry puree and pass through a fine sieve. Transfer to a pan and add the agar agar. Boil for one minute and fill the cherry molds. Let set for one hour in the fridge.
Strain the cherries in syrup and heat the syrup together with the cherry puree. Dissolve the cornstarch in a bit of water and add to the puree. Bring to a boil, cool down and add the cherries. Reserve in the fridge.