Filling:
- 3 Tbsp. butter
- 1 large onion, chopped
- 3 lbs butternut squash, peeled, seeded & cut into 1/2 in. pieces
- 1 tsp. minced garlic
- 1 tsp. salt
- 1/4 tsp. white pepper
- 2 Tbsp. chopped fresh parsley
- 4 tsp. chopped fresh sage
- 1 C (about 4 oz) hazelnuts toasted, (at 350 until golden and aromatic 5-10 min)loose skins rubbed off & coarsely chopped
Sauce:
- 3 Tbsp butter
- 1 tsp. minced garlic
- 5 Tbsp flour
- 5 C whole milk
- 1 Turkish bay leaf or 1/2 California bay leaf
- 1tsp. salt
- 1/8 tsp. white pepper
- 2 C coarsely grated mozzarella (about 8 oz)
- 1 C finely grated parmigiano-reggiano (about 2 oz)
- 12 oven-ready (no-boil) lasagna noodles
Filling: Melt butter in deep 12-in. heavy skillet over moderate heat. Add onion and cook, stirring occasionally until golden (aboutt 10 min.). Add squash, garlic, salt, and pepper, and cook, stirring occasionally until squash is just tender (about 15 min.). Remove from heat and stir in parsley, sage, and nuts. Let cool.
Sauce: Melt butter in a 3 quart heavy saucepan over moderately low heat. Add garlic and cook, stirring fo r1 min. Whisk in flour and cook, whisking or 3 min. to make a roux. Add milk in a slow stream, whisking constantly. Add bay leaf and bring to a boil, whisking constantly, then reduce heat and simmer, whisking occasionally for 10 min. Whisk in salt and pepper and remove from heat. Discard bay leaf. (cover surface of sauce with wax paper if not using immediately.)
Put a rack in middle of oven and preheat to 425. Butter 13 by 9 inch baking dish.
Assemble: Toss cheeses together. Spread 1/2 C sauce in buttered baking dish and cover with 3 lasagne noodles, leaving space between noodles (pasta will expand). Spread with 2/3 C sauce and 1/3 of filling. Top with three more noodles nad another 2/3 C sauce, one third filling, and heaping 1/2 C cheese. Repeat layering one more time, beginning with sauce and ending with cheese, then top with remaining 3 noodles, remaining sauce, and remaining cheese.
Tightly cover baking dish with buttered foil and bake for 30 min. Remove foil and bake until golden and bubbling, 10-15 min. more. Let lasagne stand for 15-20 min. before serving