Mix water with yeast, put in rest of ingredients, knead a few minutes. Gives a runny dough. Let rest at room temperature until doubles in size, 1-1.5h at 25 deg.
Wash & cut rhubarb in small pieces, mix with the 50g of sugar.
Mix butter, sugar, flour and knead with fingers only until you have small crumbles in the bowl.
Preheat oven to 175 C top and bottom heat (Ober- und Unterhitze).
Use butter to grease baking sheet, roll out dough (put wheat on it and use hands, roll should not be necessary), put rhubarb on. Be careful with the water that has settled on the bottom of the bowl holding the rhubarb. Finish with crumbles, bake in the preheated oven for 30 minutes until the dough is brownish where not covered.
3-5g active yeast
150g-200g water ~40 deg
300-375g wheat flour 405-550
1/3 tablespoon baking powder
100g wheat flour 405-550