This wonderful, strong tasting green is usually undercooked. It is true that it stays a brighter green color when undercooked; but its flavor really doesn't develop. Longer cooking yields a more interesting flavor and a soft rather than crunchy if not to say tough texture. The stalks (stems) are really are not of much use. Be ruthless cut them off and put in the mulch or save for vegetable stock.
Slow cookers are an ideal way to cook this strong vegetable. The following can be done in multiples of ingredients depending on the capacity of your machine. Timing will not vary with quantity. Incidentally, I was making it for the following day's lunch and after I made it, I fell asleep and didn't turn off the machine until morning. The very long keep warm time didn't bother it at all.
A half-pound of tops and soft stems of a large bunch of broccoli di rape tossed in the slow cooker with a quarter cup of olive oil and five cloves of peeled garlic cooked in four hours on slow cook. When taken from the machine, the garlic was mild and silky tasting of the greens and vice versa. Salt and no pepper.
Try this in an omelet--folded or flat--or with a virtuoous fish such as sardines.
As a vegetable makes enough for three to four people. In an omelet, it is a filling for four to six portions