Why the difference between lasagne and lasagna? Anyone know? 
I only realised there was the 'a' ended spelling recently. 
Italian pluralization.
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Lasagna is singular (so one sheet of lasagna)
Lasagne is plural (so multiple sheets of lasanga)
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That's the official Italian rule, but in English, I've seen them used interchangeably. Same with panini (multiple sandwiches) which should usually be panino (one sandwich). Don't get me started on shops outside of Italy advertising 'paninis' - sandwicheses (double plural).
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I know it's locally acceptable (outside of Italy), but it's incorrect....