Board Thread:General Discussion/@comment-3423279-20160110184118/@comment-3423279-20160116030904

His explanation was kinda vague in my defense, he just said that the hollow White, which was made from the souls of many dead Shinigami, is the same as the Asauchi.

But, it could be the way you described, shaving a portion of many Shinigami's souls which they can regenerate to make new Asauchi, I suppose we will never know.

It might also be that the Asauchi are just made by Oetsu as a blank template for a Shinigami's soul to fill now but the first one was made by a similar process at White, in a time where the Gotei 13's Captains weren't that caring about their subordinates.