Not a recipe as such, but again, tantalising pointers. Ishaq b. Sulaiman al-Israili via Constatinus Africanus.
p. 450 of lettuces
(…) They are more suited for eating cooked than raw, (…)
p. 453 of endives (endivia)
(…) if they are given to eat boiled with obsomagarum and oil, they are harmful; but with vinegar, they strengthen the stomach and constipate the belly.
p. 454 of celery (apio)
(…) Therefore if they are given to eat either cooked or raw, they open up stoppages, provoke urine, and tighten the belly. (…)
p. 457 of rocket
(…) if eaten cooked, it increases semen (…)
(…) They are assiduously given to eat with endives, lettuce, and purslane, for if taken alone, they generate heat, (…)
p. 458 of leeks
(…) the careful thus take them to eat after purslane, lettuce, endive and their like because their heat is tempered by those, or they are boiled and then washed two or three times and given to eat in the previous(ly described) manner. (…)
p. 464 of chard (sicla quam vulgus blita appelat)
(…) But if it is cooked in water and seasoned with vinegar and obsomagarum and caraway or with oil of unripe olives or of almonds, it is easier to digest, but nourishes less. (…)
p. 465 of cabbage
Cabbage is cold and dry in the first degree, it generates turbid and melancholy blood and gives a horrid odour. It is of two kinds: One that is similar to beets, one which is called canabit. Cabbages are also of two kinds, winter and summer cabbage. (…) Therefore so that their harm is removed, they are boiled and the first cooking water is discarded and they are cooked in another with the fattest meat of livestock (pecudis) or pigs and seasoned with coriander, pepper, cumin and garlic, and served. (…)
There is no recipe as such here, but if we read the entries together, we get an idea of some options and techniques. For example, a combination of endives, lettuce, and purslane, all cooked, would be seasoned with rocket, presumably also cooked, and served as boiled greens. Boiled lettuce is not as bad as it sounds, incidentally.
Chard would be served with vinegar and probably murri (that obsomagarum) or with oil. Cabbage would be boiled soft, cooked with fat meat, and seasoned with coriander, pepper, cumin and garlic.
The word pecudis in classical Latin means livestock and may be used in that context here (‘proper’ four-footed beasts as opposed to – shudder – pork), but in Middle Latin it is also often used specifically for sheep and goats, or just sheep. Certainly mutton would not be off base as an interpretation. And obviously, the mention – presumably interpolated – of pork here suggests to me that this text was meant for use in its place and time, eleventh-century Sicily, not merely an academic or antiquarian exercise.
Isaac Iudaeus de diaetis universalibus et particularibus, originally written in Arabic in the late ninth or early tenth century, was translated and adapted by Constantinus Africanus in the late 11th century and circulated widely in Italy and beyond soon afterwards. While the original applies to a different context, it is still reasonable to use it as a guide to the advice that Siculo-Normans would have found useful. It is an open question how much the original was altered in translation – I cannot say since I read no Arabic. However, the extensive reference to eating pork suggests that some alterations took place.