I have no idea why my roasted rhubarb doesn't work - it's the easiest recipe and I've followed it to the letter but even at 20 minutes in the oven it explodes to mush. If I could get it right then I'd give the Toasted Marshmallow cake a go, but I daren't try again.
Nigella's Toasted Marshmallow And Rhubarb Cake (from COOK, EAT, REPEAT) has layers of light sponge that are sandwiched with sharp, roasted rhubarb and frosted with a marshmallowy Swiss meringue that is lightly toasted. Nigella cooks her rhubarb in an ovenproof dish at 200°C/180°C Fan/400°F and this gives soft rhubarb that still holds its shape.
Rhubarb does vary a lot in thickness and if you have very slender stems then the cooking time could be shorter and you may want to start checking the rhubarb after 10 minutes and then check every 2-3 minutes after that to get the perfect texture. Also, the cake could be made with a different, slightly sharp, filling. Fresh raspberries are a good alternative and you don't need to cook them, simply crush them very lightly with a fork before using them for the filling. A zesty lemon curd could be another alternative.