Heat oven to 180c/fan160/gas mark4.
Prepare 20cm square cake tin by greasing and lining with greaseproof paper.
Take 50g rhubarb out and save to make icing.
Mix flour, bicarb and ginger in a bowl.
In a separate bowl put the sugars, eggs, oil and rhubarb, beat together.
Slowly add dry ingredients beating to combine.
Spoon the mixture into your baking tin and place in oven for 40-45 minutes.
Check after 30 as may need to put foil over if top browning too quickly.
Check cake cooked in middle by sharp knife into centre if comes out wet return cake to oven.
Cool cake in tin for 10 minutes before placing on tray to cool completely.
To make icing, beat butter, sieved icing sugar and vanilla extract until smooth.
Add the remaining rhubarb gradually, it may look as if split but you can add more icing sugar.
Chill in fridge until thickened and then spread on cooled cake.
Cut cake to required sized pieces and enjoy!
