Prepare the Roasted rhubarb, then cool and drain off the juices (the juice is good mixed into plain yogurt). Heat oven to 180C/fan 160C/gas 4. Line a 12-hole muffin tin with muffin paper cases. In a large bowl, beat together the sugar, oil, egg, orange zest and soured cream until there are no lumps and all are completely combined. Gently mix in the flour, then fold in the rhubarb.