Soak broccoli in buttermilk mixed with the brine from a jar of preserved lemons, and get ready for roasted broccoli like you've never had it before! The acidic buttermilk slightly tenderizes the broccoli (speeding up its roasting time a bit), and the salinity of the preserved lemon seasons it. Together, the buttermilk and preserved lemon pack such a big flavor punch that their characteristic rich, tangy notes come through in the roasted vegetable—not overwhelmingly so, but in a way that enhances broccoli’s own flavor. Think of it as: broccoli as its best self.
Note: If you don't have preserved lemon brine, blend 2 cups of buttermilk with the flesh of one preserved lemon until smooth (remove peel and seeds first). —EmilyC
Mix together buttermilk and preserved lemon brine. Place broccoli in a gallon-sized plastic zipper-lock bag. Pour in the brine. Seal the bag, pressing out as much air as possible and rotating the bag several times to thoroughly coat the broccoli in the brine. (The broccoli won’t be fully submerged.) Lay the bag flat; soak for about 1 hour at room temperature. I like to flip the bag a few times to evenly distribute the brine.
Heat oven to 425°F. Line a sheet pan with parchment.
Drain the broccoli in a colander, shaking most of the brine off. Place the broccoli and sliced red onion on the sheet pan, and toss with 3 tablespoons of olive oil and kosher salt and black pepper, to taste. (Taste a piece of the brined broccoli to guide the amount of salt you use.) Roast for about 20 to 25 minutes, or until the broccoli is tender, crispy, and charred (or less time if you like your broccoli a little crunchy). Note: the brine that clings to the florets will cause the broccoli to steam-roast in the oven, and once it evaporates, the broccoli will start to brown. Adjust seasoning to taste.
Meanwhile, in a nonstick skillet, heat 1 1/2 to 2 tablespoon of olive oil over medium heat, or enough to cover the bottom of the skillet. Add the panko, stirring to evenly coat with the olive oil. Once the panko has started to brown, add minced preserved lemon peel, sumac, and a pinch of salt. Continue to toast until the crumbs are golden brown. Off the heat, stir in the dill.
Squeeze a little lemon juice over the roasted broccoli (to taste) and toss in the sumac crumbs to evenly coat. Transfer to a serving platter or dish. Serve warm.