White Lasagna (Prosciutto and Mushrooms)

It’s not your traditional lasagna with tomato and mozzarella cheese and the ingredients are a bit on the expensive side. The prosciutto, Portobello mushrooms and the Gruyère cheese do have however are worth the expense for this special occasion dish.

Filling:
3 Tbsp. + 2 tsp. extra-virgin olive oil
2½ lbs portobello mushrooms, stems trimmed (~ 10)
1 cup prosciutto, chopped (~ 6 oz)
⅔ cup shallots, chopped (~ 2 large)
1 tsp. fresh rosemary, chopped
1 tsp. fresh thyme, chopped

Sauce:
4 cups whole milk
1 (14 oz) can chicken broth
1 bay leaf
½ cup (1 stick) butter
⅔ cup all-purpose flour, unbleached
2 cups Gruyère cheese, shredded (~ 8 oz)
⅓ cup Parmesan cheese, freshly grated
1/8 tsp. ground nutmeg

Lasagna:
1 lb lasagna noodles
½ cup Parmesan cheese, freshly grated
2 Tbsp. butter, cut into ½" pieces

Preheat an oven to 400°F (200°C/180°C fan, Gas Mark 6). Brush rimmed baking sheet with 1 Tbsp. olive oil.

For the Filling:
Toss mushrooms with 2 Tbsp. olive oil in large bowl to coat. Arrange mushrooms, gill side up, in single layer on prepared baking sheet. Sprinkle with salt and pepper. Roast until tender, about 45 minutes. Cool. Cut mushrooms into ⅓" thick slices.

Meanwhile, heat remaining 2 tsp. oil in medium nonstick skillet over medium heat. Add prosciutto; sauté until browned, about 3 minutes. Add shallots, rosemary, and thyme. Cook until shallots are tender, stirring frequently, about 5 minutes. Make-Ahead: Mushrooms and prosciutto-shallot mixture can be made 1 day ahead. Cover separately and chill.

For the Sauce:
Bring milk, broth, and bay leaf to simmer in heavy large saucepan over medium heat. Remove from heat. Let stand 10 minutes; discard bay leaf.

Melt butter in heavy medium saucepan over medium-low heat. Whisk in flour; stir 2 minutes. Whisk in hot milk mixture; bring to boil, whisking frequently. Reduce heat to low; simmer 5 minutes, stirring frequently. Remove from heat; stir in Gruyère, Parmesan, and nutmeg. Season to taste with salt and pepper.

Reduce oven temperature to 350°F (180°C/160°C fan, Gas Mark 4). Butter a 9x13x2" glass baking dish.

For the Lasagna:
Cook noodles in large pot of boiling salted water until almost tender but slightly undercooked (noodles will finish cooking in oven). Drain and rinse with cold water. Drain again; pat dry.

Spread 1 cup sauce over bottom of prepared dish. Arrange ⅓ of noodles over sauce, overlapping to fit. Spread about 1⅔ cups sauce over noodles. Arrange ½ of mushrooms over sauce. Scatter ½ of the prosciutto mixture over the mushrooms. Arrange ½ of the remaining noodles over the mushrooms, overlapping to fit. Spread 1⅔ cups sauce over noodles. Arrange remaining mushrooms over sauce, sprinkle with remaining prosciutto, and top with remaining noodles. Spread the remaining sauce over noodles, sprinkle the Parmesan cheese over top and dot with butter.

Bake in a preheated oven until the lasagna top is golden brown and the sauce is bubbling, about 45 minutes. Let stand 15-20 minutes before serving.

Makes 8 servings.