I've found several different tricks for this one all over the place but I think I have found a way to get this while actually making it worth your while. Now I don't have access to all the Books that can be found that might make this even better but what I have got going isn't too bad. Either way this trophy is going to take a while to get.
In Warrior's Roost you can battle in the arena. You have five consecutive fights (if you can beat them, doesn't matter either way) But this gives the potential to raise your eleth a fair bit.
My current set up in the order it appears in my mixer is;
Book of Potential (increase mixer's development when cooking)
Book of Satiation (when you cook something it will cook two)
Book of Gathering (increases items found)
Chicken curry (triggers if you eleth is below half) end of battle
Rice omelette (triggers if your eleth is above half) end of battle
Crab fried rice (triggers at 10 seconds in battle) during battle
Salmon and roe bowl (triggers at 30 seconds in battle) during battle
As long as you have enough eleth you can viably have three of these foods trigger each battle, the crab and salmon during and rice of chicken at the end. And because of satiation you get two each time. In just 5 battles, with around 1300 eleth I am gaining over 100 eleth for my mixer. So it is possible the growth may be even higher as you get up in eleth capacity.
There are additional books that I do not have yet that can make this process even easier and perhaps even faster so even if you wait and go back to Warrior's roost later you are good to go.
Reasons for this method over some of the other recommendations.
1. you have a turtlez merchant right beside the desk so you can quickly refill eleth after your battles
2. you easily earn enough gald to pay for refilling your eleth.
3. the rewards and possible loot from the enemies can earn a large amount of money.
4. decent experience when in the level 30-60 range