Roasted Butternut Squash and Rosemary Gratin

Bahan-bahan (4 porsi)

• 3 cups (about 3 pounds uncooked) mashed butternut squash
• ¼ cup freshly grated Parmesan cheese, (divided)
• ½ teaspoon kosher salt
• ½ to ¾ teaspoon chopped fresh rosemary
• ¼ teaspoon freshly ground black pepper
• ¼ cup shredded Asiago cheese