Cockagrice is exactly what it says on the tin: a cock (chicken) cooked with a grice (a young pig). In the 1400s, cockagrice was a fairly popular dish, to judge by its appearances in cookery books. The details of preparation differed, but in most cases it was simply a matter of cleaning the animals, binding them together, and roasting them on a spit. Some particularly ambitious cooks made quite a fanciful dish from these humble ingredients:
xxviij - Cokyntryce. Take a Capoun, and skald hym, and draw hem clene, and smyte hem a-to in the waste ouerthwart; take a Pigge, and skald hym, and draw hym in the same maner, and smyte hem also in the waste; take a nedyl and a threde, and sewe the fore partye of the Capoun to the After parti of the Pygge; and the fore partye of the Pigge, to the hynder party of the Capoun, and than stuffe hem as thou stuffyst a Pigge; putte hem on a spete, and Roste hym: and whan he is y-now, dore hem with 3olkys of Eyroun, and pouder Gyngere and Safroun, thenne wyth the Ius of Percely with-owte; and than serue it forth for a ryal mete.
-- Two Fifteenth-Century Cookery-Books, England, 1430
Cockagrice/Cockatrice: Take a capon and clean him and gut him, and cut him in two along the waist crosswise. Take a pig and clean him likewise, and cut him open also. Take a needle and thread and sew the front of the capon to the rear of the pig, and the front of the pig to the rear of the capon. Then stuff him as you would a pig; put him on a spit and roast him. When it is ready, coat him with egg yolk seasoned with ginger powder, saffron, and parsley. Serve it, for a royal meal.
There are other recipes that call for first boiling the animals together and then roasting them, and instructions for serving with daryoles and flaumpoynts and other delights. For reasons unclear this recipe does not seem to have outlasted the Tudors, although recipes such as Pork Stuffed Chicken Breasts and Bacon Wrapped Chicken Legs are still popular today.