So that’s what I bought.
My original plan was to cook it absolutely plain, over steam or in salted water, as I would have cooked a wedge of cabbage. But my tendency to tinker got the better of me, and I started to think about alternatives. I ran through the flavors associated with a corned beef dinner and stopped at American-style mustard, which often contains turmeric, more for color than anything else. But turmeric does indeed have an earthy, slightly bitter flavor that I’m fond of, and it is often used in Indian vegetable cooking, including in cabbage dishes — as is mustard seed.
This all began to make sense. Now, I didn’t want to make a plate of broccoli rabe that would scream “India,” so I avoided flavors like ginger and ghee (clarified butter). For a nice (1 1/3-pound) bunch of youngish broccoli rabe, I melted a tablespoon of unsalted butter in a deep sauté pan over medium heat, then added a tablespoon of whole brown mustard seeds and heated them until they began to emit their spicy aroma. I proceeded to pile in the broccoli rabe, cut into two-inch lengths and still damp from a thorough washing, and added a 1/3 cup of water into which I had stirred a teaspoon of ground turmeric.
I seasoned with salt (no pepper), raised the heat to medium-high and covered the pan until the greens had shrunk enough to stir them (with tongs), then continued to cook, still covered, until they were fairly tender. I removed the lid and let more of the liquid boil off, by which time the broccoli rabe was as tender as I wanted it. You will cook yours as you like, of course. I removed the vegetable to a serving dish, then continued to reduce the liquid in the pan until just a few tablespoons remained; I spooned this over the greens.
Served with the corned beef and steamed potatoes, these mustard-seed-tinged greens were not just a stand-in for the usual cabbage; they added an element all their own. They tasted zippy, and the simple spicing did not mask the broccoli rabe’s mild bitterness (and the cooked mustard seeds were fun to pop between our teeth). A similar approach would work well with many other leafy greens, too.