Preheat the oven to 180C/gas
4/fan 160C. If baking to cut into
squares, line a 33 x 23 x 5cm
baking tin with non-stick baking
parchment. If serving as a pudding
simply grease a similar-sized
ovenproof dish with a little butter.
Melt about 15g/1⁄2oz of the butter
and stir into the caster sugar, nuts
and cinnamon in a bowl. Set aside.
Cream together the rest of the
butter with the muscovado sugar
and egg. When smooth and
creamy, stir in the flour, bicarbonate
of soda, 1⁄2 tsp salt and the soured
cream. Lastly, stir in the rhubarb.
Pour the rhubarb mixture into the
prepared tin and sprinkle with the
sugar and nut topping. Bake for
30-35 minutes or until a skewer
inserted in the centre comes out
clean. Serve immediately as a
pudding, or leave to cool and cut
into squares. Keeps for 4-5 days in
an airtight tin.