What kind of pan is a half sheet pan. I googled it but it seems to be an ordinary pan. No trace of sheets, whatsoever. Why half?
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Antonia - a "sheet cake" is a big flat cake cut into squares, as opposed to a "layer cake" which has several layers of cake and filling. A "full sheet pan" is the size a bakery would use to bake a really big flat cake, and a half-sheet pan is probably the biggest flat pan that would fit in most home ovens.
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Or is baking sheet used syonymously for baking dish here?
 Mister Micawber's reply was promoted to an answer.
Thanks Mr Micawber
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 khoff's reply was promoted to an answer.
I found later that hal-sheet is smaller (of course) than full size. Thanks Khoff