Sweet potatoes aren't even potatoes (on either side of the Pond, I think). And they make a very nice muffin or bread (tea cake and cake respectively, I think, over there).Biscuits just can't contain potato of any description, that's against all laws of man, beast and nature.
Potatoes are for making crisps:
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or maybe for making chips:
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Or at a push, boiled (and possibly mashed).