Preheat the oven to 200°C/fan 180°C.
Cut the trimmed rhubarb into 2cm pieces. Put into a large baking tin and sprinkle with the sugar. Add the rhubarb juice, and the vanilla pod and seeds.
Cover the tin with foil, sealing the edges, and bake for 30 minutes or until the rhubarb is very tender and just holding its shape.
Allow the rhubarb to cool down completely before getting on with the rest.
When ready to assemble, start by gently transferring the rhubarb into another dish using a slotted spoon. Save the liquid.
Make the mascarpone cream.
Separate the eggs and set aside the yolks until needed.
Using a hand-mixer or a stand-mixer fitted with the whisk attachement, whip the egg whites with a pinch of salt until stiff. Then add half the sugar and keep on whipping until the sugar has dissolved, and set aside.
In a large bowl, beat the egg yolks with the remaining sugar until light and fluffy, around five minutes.
Now add the mascarpone, a little at a time, mixing well after each addition. Whisk together until smooth.
Add a large spoonful of the meringue into the mascarpone mixture and mix in energetically using a silicon spatula. Now add the rest of the meringue and fold in delicately until fully incorporated.
To assemble the tiramisu, prepare 6 ramekins.
Briefly soak two ladyfingers (read note above in case you want to make thinner layers) into the rhubarb syrup and arrange at the bottom of a ramekin. repeat with the remaining ones. I like to break my ladyfingers into halves.
Top with a dash of extra syrup. And a generous spoonful of the roasted rhubarb.
Finally, pipe the mascarpone cream onto the rhubarb. Cover with clingfilm and refrigerate until ready to serve.
Before serving, whisk the whipping cream with the seeds from half a vanilla pod and a dash of amaretto - if using, until lightly whipped. Spoon a dollop of the cream onto your tiramisu, and serve.