Why the cookie crumbles

I’ve make these cranberry shortbread stars every Christmas for the past ten years, and they have quite the following. They’re buttery and crumbly, with just a hint of tartness from the addition of dried cranberries. I’d give you the exact recipe, but then I’d have to kill you. 

My recipe has just six ingredients: butter, sugar, flour, cornstarch, salt and cranberries. It uses a basic creaming method. First, cream the butter and sugar until fluffy. Combine the flour, cornstarch and salt, and add it slowly to the butter. FInally, fold in the cranberries.

The two main features of shortbread are its buttery flavour and crumbly texture. Any good recipe will have a high ratio of butter to flour, which provides good flavour. The crumbly texture can be accomplished in one of two ways: by adding cornstarch, or by using a different mixing method.

Any time that flour meets water in a recipe (and there’s lots of water in butter), you create gluten. Gluten is a complex network of long, strand-like proteins that provide structure and elasticity. Sometimes you want gluten (for example, in bread) and sometimes you don’t (for example, in shortbread).

So, back to shortbread. By adding cornstarch to your mixture, you interfere with gluten’s ability to make long strands. Instead, you get short, stubby strands of gluten, and a crumbly texture.

Purists omit the cornstarch and just use butter, sugar, flour and salt. The key here is to start with all the dry ingredients in one bowl, and to cut the butter into it. The butter pieces get progressively smaller and smaller, until eventually it looks like sand and the whole mixture comes together. The overall principle is the same: the butter interferes with the gluten strands, resulting in a crumbly cookie.

Either way, it sure is tasty.

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