To prepare rhubarb: wash the rhubarb stems thoroughly; cut into 2cm pieces. Combine the rhubarb and sugar in a medium bowl. Transfer the rhubarb mixture to a colander with the bowl underneath. Cover; refrigerate for 6 hours or overnight. Add the rhubarb, juices and vanilla bean paste to a heated medium frying pan, bring mixture to the boil. Simmer, uncovered, stirring occasionally, for about 5 minutes or until rhubarb is just tender.

Preheat the oven to 150°C (130°C fan-forced). Grease 17cm x 36cm ovenproof serving plate with butter, leaving a 3cm border. Sift the cornflour over the greased area.

Beat egg whites in a large bowl with an electric mixer until soft peaks form. Gradually add the caster sugar, beating until dissolved between additions, scraping down the side of the bowl occasionally. Gradually add the brown sugar, beating until dissolved between additions. Fold in extra sifted cornflour.

Pile the meringue along the centre of the prepared plate. Use a metal spatula or the back of a spoon to spread the meringue over the greased area, making a shallow indentation along the centre.

Reduce the oven temperature to 100°C (80°C fan-forced). Bake pavlova in the lower half of the oven for 1 1/2 hours or until dry and crisp. Turn off oven; cool in the oven with the door ajar.

Combine the whipped cream and yogurt in a medium bowl. Top the pavlova with cream mixture and half the rhubarb mixture. Serve with the remaining rhubarb mixture.