Sam, bleaching damages the starches in cake flour, and in doing so increases its "carrying capacity"; the ability for it to hold together a higher ratio of sugar and fat. If a recipe calls for cake flour and you substitute something that isn't bleached, it's not uncommon to have the results you're describing. It's also quite possible that you're overcreaming your butter and sugar; too much can make for an unstable structure. Beat butter and sugar together until they look white; if you go so far that touching a mound of the mixture makes it collapse, that's too far. Susan

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