I included this in the Mastering Evocation Workbook, and it was indeed in Evoking Eternity.
In neither of these, though, do I give the exact “how,” mainly because I assumed it would be obvious, but I suppose the things that seem obvious to me confound most others. That’s not a criticism of anyone other than myself.
Now, when I’m making absinthe, I’ll measure and weight everything, using a hydrometer every step of the way, checking the distillation temperature, etc. etc. But that’s not what I do when I’m making thyme chicken breasts with balsamic-apricot drizzle. I’ll season it by look, and then by smell, and then I’ll usually toss a few extra drops of everything in just to be safe!
The former is science while the latter is art. The elixir falls into the ‘art’ category more than ‘science.’ (I’m hungry while I write this, and now I want a glass of absinthe to go with my chicken… damn).
So, what I’ll do is fill my chalice with red wine. I prefer to use manischewitz, because it’s sweet, it’s thick, it’s red, and it’s cheap.
I add a few drops of Bat’s Blood Oil (I use Anna Riva’s, despite everyone else in the world saying it’s shit. It works just fine for me!)
Note that I’ll fill my chalice if I’m doing 1 evocation. If I’m using it for intense rituals, like the Gatekeeper Ritual, I’ll fill a pitcher with the wine.
Three days prior to the ritual, I’ll collect fresh moss… which can be difficult to find, living in the desert. There are a few parts of town, mainly around parks, where trees have shaded the ditches, and moss grows there. So, I’ll scoop up a few good chunks of moss and throw it in with the wine.
If I’m only doing a single evocation, I’ll go to the pet store, purchase a rat, and harvest its blood, usually through quick decapitation. It is amazing, though, how little blood this gives me. I’ll usually have to hold it upside down and let it drip out, or squeeze the carcass until I get a bit of blood.
If I’m doing a major ritual, I’ll use 3 rats.
Sometimes I’ll add in my own blood, just a drop or two. My good friend Jhon Longshaw insists upon using semen in these concoctions. The real advantage of doing that is if you’re using the “cultivation period” as a magickal attuning, focusing your energy and intention upon the potency of the ritual, rather than at the computer screen 
Let the mixture sit for three days at room temperature. If you’re using a chalice, put a cloth or something over it. 3 days later, take it into your ritual, shake it, serve, and enjoy!
