I've noticed that the general public is unclear on the concept of streusel. American recipes calling for streusel most often give a recipe for what I call crumb topping, not a real streusel. A traditional German streusel bakes up into a kind of shortbread balls. It is crunchy and cookie-like on top and soft on the bottom where it meets the cake or fruit. Typical German streusel recipes call for a ratio of 1:1:2, sugar:butter:flour, or close to that.
In contrast, American recipes often feature a 3:1:2 or even 3:3:1 ratio (sugar:butter:flour). In the former you will finish with a sandy-like topping that shakes off easily (see picture) while the latter will meld with the sugar for a crispy, lacy effect.
As an illustration, take this recipe posted by King Arthur Flour for Cinnamon-Streusel Coffeecake. I made it last weekend and found it to be pretty good (and very sweet, another American thing). But it is definitely in the crumb topping, not real streusel division. On the other hand, this sheetcake with quark has a real streusel (1:1:1.5 by weight) and this "Russischer Zupfkuchen" has a clear 1:1:2 ratio (with a little cocoa thrown in).
Don't get me wrong, all these recipes can yield a delicious contrasting layer to a cake, but let's call them by their correct names, lest we disappoint.
Photo Cinnamon-Streusel Coffeecake © J.McGavin
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