Peel the rhubarb, cut into pieces and wash. Beat the egg whites with 200 g sugar until stiff.
Beat the margarine, egg yolks and sugar until frothy. Mix the flour and baking powder, stir in and add a little milk as needed (but not too much, it is a very firm dough).
Grease a baking sheet and spread the batter on it. Pre-bake at 200 ° C for about 10 minutes. Then spread the rhubarb over it, pour the stiffly beaten meringue on top and smooth it out. Bake at 175 ° C for another 20 minutes.