Homer provides the following recipe for kykeon:
Fair-curled Hekamede prepared a mixture, she whom the old man had brought from Tenedos, when Achilles laid it waste, the daughter of magnanimous Arsinoüs, whom the Greeks selected for him, because he surpassed all in counsel. First she set forward for them a handsome, cyanus-footed, well-polished table; then upon it a brazen tray, and on it an onion, a relish for the draught, as well as new honey, and beside it the fruit of sacred corn. Likewise a splendid cup near them, which the old man had brought from home, studded with golden nails. Its handles were four, and around each were two golden pigeons feeding, and under it were two bottoms. Another indeed would have removed it with difficulty from the table, being full; but aged Nestor raised it without difficulty. In it the woman, like unto the Goddesses, had mixed for them Pramnian wine, and grated over it a goat’s-milk cheese with a brazen rasp, and sprinkled white flour upon it: then bade them drink, as soon as she had prepared the potion. (Iliad 11.635–641)
Which Kírkē improved upon by spicing her kykeon up with dangerous herbs and honey:
And she straightway came forth and opened the bright doors, and bade them in; and all went with her in their folly. Only Eurylochus remained behind, for he suspected that there was a snare. She brought them in and made them sit on chairs and seats, and made for them a potion of cheese and barley meal and yellow honey with Pramnian wine; but in the food she mixed baneful drugs, that they might utterly forget their native land. Now when she had given them the potion, and they had drunk it off, then she presently smote them with her wand, and penned them in the sties. And they had the heads, and voice, and bristles, and shape of swine, but their minds remained unchanged even as before. So they were penned there weeping, and before them Circe flung mast and acorns, and the fruit of the cornel tree, to eat, such things as wallowing swine are wont to feed upon. (Odyssey 230-243)
However, according to Wasson, Hofmann and their cronies kykeon’s not complete without some LSD or ergot mixed in:
Albert Hofmann, writing in The Road to Eleusis, further suggested that the hierophants might have processed the C. purpurea ergot with a simple water extraction, dissolving off the water-soluble alkaloids containing ergonovine and methylergonovine, the principal hypothesised psychoactive compounds. Ergonovine, also known as ergometrine or ergobasine, is a psychoactive lysergic acid amide similar in structure to, but far less potent than lysergide, or LSD. The proposed water-extraction process would also supposedly have prevented the toxic ergopeptine alkaloids of C. purpurea, abortifacient and dangerously vasoconstrictive but not at all psychedelic, from entering the potion. Ergopeptine alkaloids such as ergotoxine and ergotamine were the agents responsible for the recurring plagues of ergotism known throughout European history, so it may safely be assumed that they were somehow excluded from the kykeon. Hofmann also proposed an alternate hypothesis that the kykeon might have been prepared from another species of ergot (Claviceps paspali), growing not on barley (or only rarely) but on wild grasses of the region such as Paspalum distichum. The hypothesis appeared attractive because C. paspali produces a much more psychedelic blend of alkaloids than C. purpurea, similar to that contained in the redoubtable Western hemisphere psychedelic plant of the Aztecs, ololiuhqui. In addition, the toxic ergopeptine alkaloids are largely if not completely absent in this ergot species. (Peter Webster, Mixing the Kykeon)
Begin by boiling some barley, and then strain the water out. Into the barley-water mix some fresh mint, honey, lemon or pomegranate juice and any of the above you wish. You probably shouldn’t add ergot, as that’s just some stupid shit some ivory tower academics pulled out of Dionysos only knows where and LSD only if you’re already experienced and all the participants are duly informed ahead of time, can consciously and responsibly consent, there’s crash space and a ground crew to help them come down. Be careful about mixing with wine or other entheogens, or herbs such as pennyroyal.