The only thing I might like better than Brussels sprouts roasted to a crisp are thinly sliced raw Brussels sprouts dressed with a bright vinaigrette and toasted nuts. This salad takes a little more time to make than the usual shaved sprouts salad, but the extra work is worth the flavor and texture combination of nutty brown butter vinaigrette, crunchy Brussels sprouts, crisp slices of sweet apple and toasted hazelnuts. And unlike most salads, it tastes even better the day after it's made.
This salad recipe involves two types of cooking: toasting (and peeling) the hazelnuts and browning the butter. The first is done in the oven, until the nuts turn golden and their brown skins begin blistering. Rubbed in a clean dish towel, they give up most of their skins, but you'll probably find that some of the nuts stay stubbornly unpeeled. Since this is a salad, not a delicate cookie recipe, this isn't an issue, and I like the color contrast the skins lend.
Browning the butter doesn't take long, but can be a little intimidating if you haven't tried it before. (The recipe describes the process, but here are more detailed instructions if you need them.) I don't strain the finished butter because I like the toasty flavor all the browned bits add, and I use a flavorless oil like grapeseed instead of olive oil in the vinaigrette, because I don't want anything competing with its nutty richness.
If you have a mandoline, now is the time to break it out. Not only will it make prepping the ingredients much easier and quicker, it is the only way to get consistently thin slices of brussel sprout and apple, which will give the finished salad a better texture. If you are a kitchen ninja with a very sharp knife, you may be able to come close, but if I were you, I'd just buy a Benriner. It costs about $20 and I use mine at least once a week.
Eaten within a few hours of making it, the salad is crunchy and refreshing, but I actually prefer the flavor and slightly softer texture after it sits in the refrigerator overnight. The Brussels sprouts are softened but not soggy, the apple slices still crisp, and all the flavors have mellowed together: sweet, toasty, a little bitter and green. However far ahead you assemble it, make sure to let the refrigerated salad sit at room temperature for about 30 minutes before serving, so the butter in the dressing has time to soften up.
That's right. Butter in the salad dressing. It must be the holidays.
Preheat the oven to 350°F. Spread the hazelnuts on a rimmed sheet pan and toast for 10-15 minutes, or until nuts are lightly golden and skins are peeling away. Wrap nuts in a clean dish towel and let steam for a minute. Rub nuts with the towel to remove as many skins as possible. (Not all of the skins will be removed, which is fine.) Roughly chop the nuts and set aside.
Shave the Brussels sprouts by gripping the stem end with your fingers and using a mandoline to slice as thinly as possible down to the stem, or until the sprout is too short to safely slice. (Alternatively, you can use a food processor to shave the sprouts. Trim and discard the stems and use the slicing blade of the food processor to finely shred the sprouts.) Place shaved sprouts in a large mixing bowl. Halve and core the apple, then use the mandoline to cut into slices about 1/4-inch thick. Place apple slices in a small bowl and toss with 2 teaspoons lemon juice to prevent browning.
Have a small Pyrex or other heatproof liquid measuring cup ready. Melt the butter in a small saucepan over medium heat. Cook, swirling occasionally, until butter is dark brown and smells nutty. Immediately pour into the measuring cup to stop the cooking. Let cool slightly.
In a small bowl, whisk together the vinegar, remaining 2 teaspoons lemon juice and salt. Slowly drizzle in the brown butter, whisking constantly, until dressing is thick and emulsified. Repeat with the grapeseed oil. Taste for seasoning. Pour the dressing over the Brussels sprouts and mix in thoroughly with your hands. Add the apples and nuts and mix.
Salad can be assembled ahead of time and refrigerated for several hours or up to overnight. Let sit at room temperature for 30 minutes before serving. If making more than 2 hours ahead, add the nuts just before serving for best texture.