Wash the cherries in cold water and remove the stones without cutting the cherries entirely in half. Place into a large bowl and set aside.
Put the caster sugar and 150ml/5fl oz water into a saucepan. Add the bay leaves and thyme sprigs and place onto a medium heat. As soon as the syrup begins to boil pour it over the cherries and set aside to cool down. (If the cherries are not very ripe, add them to the boiling syrup and poach for 2 minutes, then pour into a bowl to cool down.)
For the meringues, preheat the oven to 100C/200F/Gas ¼ and line a baking sheet with baking parchment.
Beat the egg whites with the caster sugar until stiff peaks. Add the icing sugar and continue to beat for 4-6 minutes, or until the mixture is smooth and shiny.
Drain the cherries onto kitchen paper to remove as much syrup as possible. Using a large spoon, fold the cherries lightly into the meringue mixture. Using another larger spoon as well, shape a quenelle of the mixture and place it onto the lined baking sheet. Repeat the process to make three more meringues. Place into the oven and cook for two hours.
Once cooked, remove from the oven and allow to cool slightly before removing from the baking tray using a palette knife. Transfer to a cooling rack and set aside.
Place the rhubarb into a saucepan with the sugar, vanilla and 100ml/3¾fl oz water. Slowly bring to the boil and cook gently until the rhubarb is soft enough to crush with a spoon.
Remove the vanilla pod and tip the mixture into a processor and blend for two minutes. Once smooth, pass the purée through a fine-meshed conical sieve into a bowl. (Add a little cold water to thin the coulis, if neccessary.)
To serve, place the meringue onto a plate and spoon the rhubarb coulis around the edge.