Butternut Squash Gratin With Goat Cheese And Hazelnuts

3

1/2 pounds butternut squash (about 2 medium), peeled, seeded, cut into 3/4- to 1-inch cubes (8 cups)

2

tablespoons olive oil

Coarse kosher salt

4

tablespoons (1/2 stick) butter, divided

3

cups sliced leeks (white and pale green parts only)

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