Preheat the oven to 160° C w/ fan.
Melt the butter & set aside for cooling down.
Trim & clean & chop the rhubarb; you'll need 200 g chopped rhubarb.
Line a loaf tin w/ baking parchment.
Whisk together molten butter, yoghurt, sugar, eggs & vanilla essence w/ your handheld electric mixer.
Mix flour & baking powder & salt; add the butter mess & mix.
Fold in the rhubarb & pour the mess into the prepared loaf tin.
Let it bake at 160° C w/ fan for about 50 min. Make the famous test w/ the wooden pin ...
Let the cake cool down for 10 min; afterwards lift the cake out of the baking tin.
After another 10 min remove the baking parchment - carefully.
Wait until the cake is at room temperature; it's about further 40 min.
For the icing combine the lemon juice & the icing sigar.
Spoon the icing all over the loaf.