ink Restaurant - Berkshire Pork Tenderloin with Charcoal Crust
The only mention of "charcoal" in his book is a charcoal vinaigrette ...
The charcoal part is made by placing nori sheets on a rack, then the rack inside a sheet pan, then place another rack on top of the nori sheets to keep them flat.
Bake in 400 degree oven until completely burned and charred (about 1 hr)
Then he mixes it into the vinaigrette. ( but you would omit that part)
Hope this helps!