Cheesy Roasted Cabbage Wedges

Name: Cheesy Roasted Cabbage Wedges
Ingredients: ½ cup blanched hazelnuts; Extra-virgin olive oil (for baking sheets); 1 large head of savoy cabbage (about 3 lb.); 6 oz. Gruyère, coarsely grated (about 1½ cups); 1 Tbsp. cornstarch; 1⅔ cups (or more) heavy cream; 2 Tbsp. Dijon mustard; 2 garlic cloves, finely grated; 1½ tsp. finely grated lemon zest, divided; 1 tsp. Diamond Crystal or ½ tsp. Morton kosher salt, plus more; 1 tsp. freshly ground pepper, plus more; 5 oz. Parmesan, finely grated (about 3 cups), plus more for serving; ¼ cup finely chopped parsley