Epicurious’s Joe Sevier explains the appeal of charred food:

“Burning foods on purpose is nothing new. In classic French cuisine, stocks are often started by cutting an onion in half and then searing the exposed flesh until the surface is totally black. The blackened onion then goes into the pot with roasted animal bones and other aromatics to simmer away. When I was in culinary school, we learned that this was a key component of a certain type of dark stock: the blackened onion not only adds flavor, imparting a subtle bitterness that offsets the sweet taste of carrots, tomato paste, and whatever else might be in the stock. It also lends a rich color, which makes the stock look more appealing.”