There are three key things to keep in mind here. The first is char: Do not be afraid to take these vegetables to the edge of burnt. Both cauliflower and...
There are three key things to keep in mind here. The first is char: Do not be afraid to take these vegetables to the edge of burnt. Both cauliflower and cabbage taste amazing with very dark edges; don’t skimp on them. The second is speed: The moment you mix the vegetables with the dressing, it will begin to soften. It’s still crazy good but the magical moment is when it just begins to soften and each bite is both crackly and tender. The third is yield. This doesn’t make a lot, in the end, because the vegetables shrink so much when they cook. But you’re still limited to what you can fit on a sheet pan. That works out to one generous or two moderate portions. You’ll likely lop off part of your cabbage and cauliflower and wrap the rest up in the fridge for another day, but since this is so good, that day will probably be tomorrow.
Heat oven to 450°F. Cut cabbage into 1/2-inch ribbons, then cut the ribbons into 1- to 2-inch segments. Cut cauliflower into 1/2- to 1-inch chunks (i.e. quite small). On a large baking sheet, toss with olive oil until lightly coated (about 2 to 3 tablespoons) and sprinkle with salt and pepper.
Roast for 10 minutes, then remove the pan from the oven just long enough to toss everything around so it colors evenly. Return to the oven for 5 minutes, toss again, and 5 final minutes if needed. Don’t be afraid to get some serious char on the vegetables. They will taste good, not burnt.
Meanwhile, make the dressing in a large bowl. Whisk garlic, lemon, tahini, and olive oil together, then whisk in water, 1 tablespoon at a time, until it reaches a thick dressing consistency — I rarely need more than 2 tablespoons. Season well with salt and black pepper, or red pepper flakes. For more heat, you can add harissa directly to the dressing to taste, but I love having it on the side of my plate in a dollop.
As soon as the vegetables are crispy, charred, and ready, add them to the bowl with the dressing, toss to coat, and eat right away.