Drain the two glasses with the morello cherries through a sieve, collecting the juice in a large saucepan. Stir the pudding powder into the collected juice and bring to the boil, stirring constantly. The juice is milky pink at first, then turns dark red and clear. Remove from the stove and immediately mix in the cherries and strawberries (or the berry mixture). Pour into a bowl and let it cool down.
This goes well with vanilla ice cream, vanilla sauce or even cream (liquid and whipped).