(Replaces in the third paragraph pan-fried eggs with scrambled eggs) By Francesca Piscioneri ROME (Reuters) -Food is a serious business in Italy, part of the national identity, as illustrated by a row that has broken out over how to make carbonara pasta sauce. Luca Cesari, a food historian and author from Bologna, faced a stream of online abuse after he posted a video on Instagram in which he presented what he said was the original version of carbonara, considered a classic of Roman cooking. Ditching the usual ingredients of Italian pecorino cheese and cured pork cheek to be mixed with eggs to…