Hi Ruth, we think you're better off sticking to the Brioche Recipe as written, unless you have a sourdough brioche recipe that has already been calibrated to include sourdough. Brioche is a special dough, and it may not work quite as well with the addition of sourdough starter. It's possible that the Naturally Leavened Kugelhopf recipe might work, but we haven't tried it with this variation. 

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