Preheat oven to 400° F.
Heat the hazelnuts in a skillet over medium-low heat. Cook, stirring frequently, until nuts just start to turn a little brown and smell fragrant. Transfer the nuts to a plate to cool.
Place butternut squash, olive oil, salt and pepper in a large bowl and toss to coat evenly. Transfer the seasoned squash onto a baking sheet and roast until just tender and beginning to brown, about 25 minutes. Set aside.
Reduce the oven to 375° F.
In a sauté pan, heat 3 tablespoons of butter over medium heat and add the onions or leeks, sage, thyme, and nutmeg. Cook 15 minutes, or until onions/leeks are soft. Remove from the heat and stir in the spinach.
Butter a 9×13” baking dish; spread half of the onion mixture over the bottom. Next layer half of the squash and half of the goat cheese. Repeat the layering with rest of the onions/leeks, squash, and goat cheese. Pour the half and half over the gratin. Coarsely chop the hazelnuts and sprinkle them over the top. Bake uncovered until bubbling, about 35 minutes.
Source: Chef Lynda Lacher, Therapeutic Chef