Darn. I did not try hard enough to discover their secret!
They do vacuum seal 3 whole heads of romaine with only the outer leaves removed. It is cooked sous vide at 68°C for 18 minutes with 90 g of unsalted, cubed butter. After being sous vided they are sliced lengthwise and served with salted and dried grated egg yolk and dried broken olives as part of a dish.
I shall try again.