I am about to become part-owner of a wood supply business, and one of their specialties is large slabs like that one. They have a couple of very large custom rigs for milling the raw wood dead flat with parallel faces. The slabs are then offered in that form, requiring fine sanding, a finish, and legs. But they'll also pre-finish and/or add legs as asked. Quite the sight, a room full of those!

If all goes well, I do hope the next worktable in my office here will be a live edge slab.

Cheers!