Heat the butter in a large 12-inch skillet over medium-high heat until foaming. Swirl to coat the bottom of the skillet.
Add the broccolini and season it with kosher salt, black pepper, and garlic powder.
Sauté the broccolini for about 2 minutes on each side until it has absorbed most of the butter.
Check to see if the stems are fork-tender. If they are, you're done! If they're still tough (this happens with relatively thick stalks), add 2 tablespoons of water to the skillet, cover it, and steam the broccolini until the stems are tender-crisp, 1-2 minutes.
Serve immediately. If there are liquids on the bottom of the skillet, remove the broccolini with a slotted spoon. You can serve it with lemon slices if you wish.
Video
Notes
How long you'll need to saute (and then steam) the broccolini will depend on how thick the stems are. As you can see in the photos and video on this page, the broccolini I used today had thin stalks, so it was ready fast. Thicker stalks will require a slightly longer cooking time. In fact, if the stems are very thin, you can skip steaming altogether and simply saute the broccolini for 2-3 minutes on each side. Check the stems - if they're fork-tender, they're ready to serve. I don't like to keep the leftovers. They tend to become a bit limp and soggy in the fridge. So I try to make just as much as we can eat immediately. But if you end up with leftovers, you can keep them in the fridge in an airtight container for up to 4 days. You can reheat them in the microwave.