Butternut Squash Gratin without water crumbs

6 cups butternut squash (peeled and cubed into about 1/2-inch pieces) 2 -3 tablespoons butter (can use oil) 2 large leeks , thinly sliced 2 granny smith[...]

2 1/2 tablespoons oil, divided 1 (20 ounce) butternut squash, sliced into 1/8-inch thick pieces salt and pepper 1/8 teaspoon ground nutmeg , divided 1 1/2[...]