Currently, it takes a barter for a single use recipe from the Dol Amroth rep vendor for a single use recipe for a specific essence type. The essence recipes are gated behind ally for the 'ratings' essences, and kindred for the 'mainstat' essences. Pretty standard stuff for recent lotro rep grind, though at present the recipes are not bind on acquire or rep gated themselves (so presumably you could trade to a crafting alt, friend, etc).
The ingredients are where it gets interesting, as it requires a lvl 50 crafting extract item (forget the name), which currently is store only. Presumably since the item has a ilvl, it will be available elsewhere. The essences also require a purple quality output of a fangorn single use rep recipe as an ingredient. The example being thrown around in /world was an essence of critical defense required 3 top tier eorlingas ingots, the (currently) store only 'extract' item, and a Fangorn skirmish shield of force. Now I don't know if a teal quality of that same shield is also usable as an ingredient, but either way we are currently looking at a double grind to make these items through crafting. Not only is there the grind for rep and barter items to acquire the actual recipe, but you have to grind out now obsolete rep faction's rep/barter currency to make this, or potentially use a weeklong guild cooldown on an obsolete item to be an ingredient in the new recipe.
I get the thought process on the essences: we're 'extracting' the essence of an item (shield = critical defense, makes some sense) to get that essence in its pure form to put in a new armour piece. Why can't you leave it to a single rep/currency grind however, and just require one of the non-barter/non-single use shield recipes as the required ingredient along with the 'traditional' craptastic grind of the recipe for the essence? Also, currently each crafting profession only has access to 2 or 3 essence recipes each, meaning for example if you're a hunter who is a jeweler, and want to craft essences for agility and crit rating (probably your 2 most important stats), you're up a creek without a paddle. Especially since some of these rating stats are MASSIVELY more valuable than others. Who is going to want to trade their highly valuable to pretty much every class crit essence for an essence from the poor schmuck who's profession only lets them make resistance and fate essences? Consider making only 1 essence recipe for 'rating' essences, and 1 recipe for mainstat essences, and give the recipes multi-outputs so a user can pick whichever rating or mainstat fits their personal needs.