In a bowl mix all ingredients. As regard to milk, add as much so the dough is in a pourable form. Thus pour on a baking tray covered with baking paper and spread evenly over the tray.
Peeled rhubarb cut into small pieces and evenly place ontop of the dough. At last make the crumble from flour, butter and sugar, then sprinkle the cake with.
Bake in pre-heated oven at 170°C for about 20-30mins.
When cooled down the cake is ready to be served.