Butternut squash gratin with aged gouda and toasted hazelnut topping

Name: Butternut squash gratin with aged gouda and toasted hazelnut topping
Ingredients: 1 small butternut squash, about 1 1/2 pounds whole; 1 good-sized parsnip, peeled and cut into small chunks, about 1/2 inch; 1 large leek, cleaned and cut into 1/2 inch pieces, white and light green part; 3 tablespoons olive oil; 3-4 cloves garlic, chopped; 1 sprig fresh rosemary, stem removed; 1/2 cup good white wine; 1/2 teaspoon sea salt; freshly ground pepper to taste; 1/2 cup good whole grain bread crumbs; 4 ounces shredded aged gouda cheese; 1/3 cup chooped, toasted hazelnuts; 3 tbsp crème fraiche; 2 tablespoons unsalted butter