Preheat the oven to 160C/320F/Gas 3.
For the rhubarb, cut two rhubarb stalks into 1cm/½in pieces. Place in a saucepan with two thirds of the sugar and a few tablespoons water. Melt the sugar over a gentle heat to form a syrup. Remove from the heat and set aside.
Cut another rhubarb stalk into 1cm/½in pieces and place in rows on a baking tray. Sprinkle over the remaining caster sugar.
Use a vegetable peeler to remove 8-12 strips from the final stem of rhubarb. Glaze with the syrup then place over the sugar coated rhubarb. Cook in the oven for 6-7 minutes, or until the rhubarb is tender.
For the custard, in a large heatproof bowl beat the egg yolks and sugar together until well combined. Add the cream and milk to a saucepan and bring to the boil.
Sit the bowl of yolks and sugar over a separate pan of gently simmering water and whisk the cream mixture into it. Add the cornflour paste and stir continuously until the custard starts to thicken.
Add the vanilla seeds to the mixture and keep stirring until the custard is thick enough to coat the back of a spoon. Remove the bowl from the heat.
In wine glasses, add a layer of the stewed rhubarb syrup and a layer of custard. Place in the fridge overnight to set.
For the crumble, preheat the oven to 180C/350F/Gas 4. Line a baking tray with baking parchment.
Rub the flour, butter, sugar and almonds together until the mixture resembles breadcrumbs.
Sprinkle the mixture onto the lined baking tray and bake for approximately 15-20 minutes, turning occasionally, until the crumble is crunchy and golden-brown. Remove from the oven and set aside to cool completely.
Once the rhubarb and custard has set, top with baked rhubarb pieces and some almond crumble. Decorate with the glazed rhubarb strips.