Butterstreuselkuchen (Butter Crumb Cake)
rec.food.baking/Naomi Lewin, WKYU-FM/Public Radio (1996)

I lived in Germany (studying) for a couple of years, and this recipe is from my friend Ortrud's mother, so it's as authentic as you get. I have translated it from weight to volume measurement (as well as from German to English).

Dough:
1 package active dry yeast
1/2 cup lukewarm milk
1/4 cup sugar
2 cups flour (+ a bit more as needed)
6 Tbsp. sweet butter
pinch salt
1 egg
grated rind of 1 lemon

Dissolve yeast in milk, adding 2 Tbsp. sugar and 1/4 cup flour. Let rise in a warm place about 25 minutes. Cream butter and remaining sugar. Blend in egg. Add salt, lemon rind, remaining flour, and yeast mixture. Mix well and knead, adding more flour as needed until dough is smooth and elastic. Cover dough and let rise in a warm place until doubled in bulk.

Topping:
7/8 cup sweet butter (chilled)
7/8 cup sugar
1 tsp. vanilla (or 1 pack vanilla sugar)
2 cups plus 1 Tbsp. flour
(optional fresh fruit)

Mix sugar and flour together, then set aside 1/4 of the mixture. Cut butter into chunks and work it into the larger quantity of sugar/flour mixture with your fingers. Blend in the reserved sugar/flour mixture gradually as needed to make good streusel clumps.

To assemble the cake, stretch the risen dough over a lightly greased cookie sheet. You can put a layer of fresh fruit on next if you want (raw rhubarb is the best -- even people who don't like rhubarb like this cake). Then distribute the streusel topping evenly over the dough. (I usually sprinkle a tiny bit more sugar on top if I have used rhubarb.)

Bake at 425 degrees for 10 - 15 minutes.