1 1⁄2 sticks butter
4 small shallots, finely chopped
3 cloves garlic, minced
1 cup chopped onion
3 teaspoons fresh thyme leaves
1 pound portobello, shiitake, or a combination of wild mushrooms, stems removed, cut into 1/2-inch chunks
1⁄2 cup white wine
1 cup chicken stock
Sea salt and freshly ground white pepper
8 cups cubed, dried brioche, crusts removed (country bread can be substituted)
1⁄4 cup chopped parsley leaves
3 sage leaves, chopped
3⁄4 cup hazelnuts, halved and lightly toasted
3 extra-large eggs, beaten
2 cups heavy cream
1 teaspoon hazelnut oil (optional)