Heat the oven to 175 C (350 F)
Chop the rhubarbs in roughly 1 cm thick pieces (I used a mandoline)
Take a small bowl and mix flour, baking soda, vanilla and salt. Set aside
In another bowl blend together butter, sugar and then the egg
Use a hand mixer with the dough hooks to blend in the milk and the small bowl with flour.
Stir in the chopped rhubarbs
Grease a baking dish of around 20 cm x 30 cm and fill it up with the cake batter
Use the small bowl to mix the topping (sugar and cinnamon)
Sprinkle topping evenly over the cake before baking it in the oven for around 35 min or until a tester comes out clean