Removing the crumb and rebaking

I'm reading a book called Bread: A Global History, by William Rubel. In it he goes over a pretty brief history of bread and then recounts his experiences with bread around the world. There are a few recipes in the back which I'll probably get to eventually, but I just ran across something that interested me. I did a search here but I guess my searching skills aren't up to par this morning, so figured I'd post.

He mentions there's a tradition in Mexico, and documented historical practice in France, of removing the crumb from a baked loaf, sprinkling it with something like sugar or alcohol and then baking it again. That's all the book says. I'm not sure whether he means the crumb gets sprinkled with whatever and rebaked or the crust does. It seems to me the crumb would get that treatment, but there's no clarification. I figured I'd try it with the crumb of my next loaf. It seems....interesting.

Does anyone here have experience with this? Any pointers, advice, comments, or opinions?