Heat the cream, vanilla, and honey in a saucepan over low heat. Squeeze the excess water from the gelatin and add it to the cream mixture. Divide the mixture between six 200ml dessert pots, then refrigerate for about 4 hours to set.
To make the crumble, rub the butter into the flour, then mix in the sugar, salt, cinnamon, and oats; spread the mixture onto a baking tray and bake at 180°C (350°F) for 25 minutes until crisp, then allow to cool.
Halve the plums and remove the stones. Place them in a baking dish with the sugar, orange juice, and a little water; cook for about 15 minutes, then add the blackberries and cook for another 12 minutes before allowing to cool.
To serve, briefly stand the pots in warm water and turn the contents out onto a plate; serve with the plums and blackberries, sprinkled with the Welsh crumble.