Prepare a batter from the ingredients margarine to baking powder. Grease a springform pan (24 or 26 cm) and dust with flour. Pour in the batter. Insert the rhubarb pieces vertically into the dough from top to bottom.
Bake at 170 ° C on the 2nd rack from the bottom for about 1 hour (stick test). Cover with parchment paper towards the end of the baking time if the cake turns dark too quickly. Let the cake cool down in the tin for a while, then slide it onto a cake plate with a cake server.