1 cup large pecan halves
¼ cup pure maple syrup
½ teaspoon plus 1 tablespoon kosher salt, plus additional for seasoning
¼ teaspoon freshly ground black pepper
¼ cup whole grain Dijon mustard
2 tablespoons apple cider vinegar
2 tablespoons fresh lemon juice
1 tablespoon granulated sugar
¼ cup vegetable oil
1½ pounds brussels sprouts, trimmed
1. Preheat oven to 325 degrees F. Spray a large sheet of foil with nonstick spray. Place pecans on small rimmed baking sheet. Whisk maple syrup, ½ teaspoon kosher salt, and ¼ teaspoon ground black pepper in a small bowl. Add to nuts and toss to coat; spread in single layer. Bake nuts 5 minutes. Stir. Continue to bake nuts until toasted and glaze is bubbling thickly, about 6 minutes. Immediately transfer nuts to prepared foil and separate. Cool completely. DO AHEAD: Can be made 2 days ahead. Store airtight.
2. Whisk mustard, vinegar, lemon juice, and sugar in small bowl; whisk in oil. Season with kosher salt and pepper.
3. Bring large pot of water to boil. Add 1 tablespoon kosher salt. Add brussels sprouts. Cook until crisp-tender and still bright green, about 5 minutes. Drain; rinse with cold water. Cool on paper towels. Using processor fitted with 1/8- to ¼-inch slicing disk, slice brussels sprouts. (You can also use a sharp knife to slice thinly.) Transfer to large bowl. DO AHEAD: Dressing and brussels sprouts can be made 1 day ahead. Cover separately; chill.
4. Toss brussels sprouts with enough dressing to coat. Let marinate 30 to 60 minutes. Mix in some pecans. Place slaw in serving bowl. Top with remaining pecans.