Brussels Sprouts with Walnut Vinaigrette

Name: Brussels Sprouts with Walnut Vinaigrette
Ingredients: 3 3/4 cups brussels sprouts, halved, cored, leaves separated; Kosher salt; 1/2 cup walnut halves, divided; 2 1/2 tablespoons unsalted butter; 1 tablespoon walnut oil plus more for drizzling; 1 medium shallot, minced; 3 tablespoons plus 2 teaspoons Champagne vinegar; 1 1/4 teaspoons Dijon mustard; Pinch of sugar; Freshly ground black pepper; 1/2 medium head of radicchio (about 5 ounces), cored and thinly sliced; Parmesan (for shaving); 3/4 teaspoons finely grated lemon zest