Rhubarb and white chocolate squares

Makes 9 500g rhubarb, trimmed 400g white chocolate, broken into pieces 1 tbsp caster sugar 150g melted butter, plus extra for greasing 200g light brown soft sugar 2 eggs, plus 1 yolk 250g plain flour sea salt Preheat the oven to 200°C/gas mark 6. Roughly chop the rhubarb sticks into 3-4cm pieces, halving lengthways if very thick. Place the rhubarb pieces on an oven tray and sprinkle with the caster sugar. Bake for 15 mins, allow to cool and reserve any juices. Turn the oven down to 180°C/gas mark 4. In a large bowl, mix together the melted butter and brown sugar until combined. Beat the eggs and egg yolk into the mixture until smooth. Fold in the flour, a pinch of salt and two-thirds of the broken chocolate, then mix in half the cooled rhubarb. Grease and line a 24 x 24cm oven tray with baking paper. Transfer the mixture into it, spreading it out with the back of a wooden spoon to fit the tin. Scatter with the remaining chocolate and remaining baked rhubarb pieces, then drizzle over the reserved rhubarb syrup. Bake for 20 mins, then cover the tray loosely with tin foil and bake for a further 20-25 mins until slightly browned and loosely firm. Allow to cool, cut into squares and serve.