Baked rigatoni with mushroom ragout

Mmmm, baked pasta. I used rigatoni, but ziti or penne would work just as well. I also used this recipe from Bon Appetit, without the dried mushrooms; I had a big clamshell of white button mushrooms from Costco which I used up instead.

It's almost mac and cheese with mushrooms added in; but the sauce is a white bechamel sauce, instead of a cheese sauce. Regardless, it's rich and cheesy and mushroom-y and delicious.

6 tablespoons (3/4 stick) butter
1 3/4 cups finely chopped onions
1 lb fresh button mushrooms, chopped
2 1/2 tablespoons all purpose flour
2 1/2 cups whole milk
3/4 cup freshly grated Parmesan cheese
1/2 cup finely chopped fresh chives
12 ounces pasta (rigatoni, penne, or ziti)
1/2 cup fresh breadcrumbs

Melt 3 tablespoons butter in heavy large skillet over medium-high heat. Add onions and sauté until soft, about 5 minutes. Add mushrooms and simmer over medium-high heat 10 minutes.

Melt remaining 3 tablespoons butter in heavy medium saucepan over medium heat. Add flour and stir constantly until golden, about 2 minutes. Gradually whisk in milk. Stir until sauce thickens and boils, about 3 minutes. Stir into mushroom mixture. Simmer 2 minutes, stirring occasionally. Stir in 1/2 cup Parmesan cheese and chives. Season sauce to taste with salt and pepper. Set aside. 

Preheat oven to 425°F. Butter 13 x 9 x 2-inch glass baking dish. Cook pasta in large pot of boiling salted water until tender but still firm to bite. Drain well. Return to pot. Add mushroom sauce and toss well to coat. Transfer to prepared baking dish. Sprinkle breadcrumbs and remaining 1/4 cup Parmesan over. Bake casserole until heated through and light golden, about 25 minutes.