Leeks Mimosa with Toasted Hazelnuts

Name: Leeks Mimosa with Toasted Hazelnuts
Ingredients: 6 large leeks (3 pounds), white and pale-green parts only, halved lengthwise and rinsed well; Coarse salt and freshly ground pepper; 2 large eggs; 1 teaspoon Dijon mustard; 2 teaspoons finely grated orange zest, plus more for garnish; 3 tablespoons fresh orange juice; 1 tablespoon fresh lemon juice; 1 tablespoon minced shallot; 3 tablespoons extra-virgin olive oil, plus more for brushing; 1 ounce (1/4 cup) skinless hazelnuts, toasted and chopped