Rhubarb & Custard Cake

Another one from Good Food Magazine (May), I love getting home to find my new copy has been delivered - I spend the next few hours salivating over the pages! Luckily I could still read the following recipe...

For the roasted rhubarb:
400g rhubarb
50g caster sugar

For the cake:
250g butter, softened
150g pot ready made custard (not the chilled kind)
250g self-raising flour
1/2 tsp baking powder
4 eggs
1 tsp vanilla extract
250g golden caster sugar
icing sugar, for dusting

Heat oven to 200C/fan 180C/gas 6. Rinse the rhubarb and shake off the excess water. Trim the ends, then cut into little-finger-size pieces. Put in a shallow dish or a baking tray, tip over the sugar, toss together, then shuffle the rhubarb so it's in a single layer. Cover with foil, then roast for 15 mins. Remove the foil. The sugar should have dissolved, so now give everything a little shake, then roast for 5 mins more or until tender and the juices are syrupy. Test with a sharp knife; the rhubarb should feel tender, not mushy, and still have kept its shape. Let it cool completely.
Butter and line a 23cm springform cake tin. Heat the oven to 180C/fan 160C/gas 4. Reserve 3 tbsp of the custard in a bowl. Beat the rest of the custard together with the butter, flour, baking powder, eggs, vanilla and sugar until creamy and smooth. Spoon one-third of the mix into the tin, add some of the rhubarb, then dot with one-third more cake mix and spread it out as well as you can. Top with some more rhubarb, then spoon over the remaining cake mix, leaving it in rough mounds and dips rather than being too neat about it. Scatter the rest of the rhubarb over the batter, then dot the remaining custard over. Bake for 40mins until risen and golden, then cover with foil and bake for 15-20mins more. It's reeady when a skewer inserted into the middle comes out clean. Cool in the tin, then dredge with icing sugar when cool.