Butternut Squash Gratin with Goat Cheese and Hazelnuts

Ingredients

• 3 1/2 pounds butternut squash (, peeled and cubed)
• 2 tablespoons olive oil
• Coarse kosher salt
• 4 tablespoons (1/2 stick) butter, divided
• 3 cups sliced onions
• 1 1/2 teaspoons chopped fresh sage
• 1 5.5- ounce log soft fresh goat cheese
• 1 cup heavy whipping cream
• 1/2 cup hazelnuts (, toasted, husked, coarsely chopped)