As far as I know, this is the standard way of making Hamentaschen these days, but it apparently wasn't always the case, and it seems this is at least not the ideal for a separate reason. That being the case, is there any source that justifies this method of making the "corners"?
closed as too localized by msh210♦ Feb 28 at 18:36
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So your question is actually if there is din "Ta'aseh V'lo Min Ha'Asui" and simply there is not Din like that because when Haman's evil verdict came out Mordechai did not make a new Queen Esther to save the Jews, but on the other hand Esther had everyone fast for 3 days but were they not already in aveilut beforehand? Now they might have been in aveilut but that was not fasting and so there is no din of "Ta'aseh V'lo Min Ha'Asui"' and more so, just like how Haman's perfect plan was destroyed, piece by piece, so should one make Hamentashen in balls and essentially "ruin" them by making three coreners, but of course you have to have Kavanah from the beggining and when you make the corners you have to say the brachah: "ברוך אתה ה', אלוקינו מלך העולם, אשר קישנו במצוותיו ולא ציוונו על הכנת אוזני המן", and of course make sure to have a gragger at hand.