Baked Rigatoni with Gorgonzola and Radicchio

Bring a large pot of generously salted water to a boil over high heat. Add the rigatoni and cook until al dente according to the package directions. Drain well in a colander, rinse under cold water and drain again. Transfer the pasta to a large bowl. Set aside.
 
Preheat an oven to 375°F (190°C).
 
In a large fry pan over high heat, warm the olive oil. Add the onion and sauté until translucent, about 4 minutes. Reduce the heat to low and season with salt and pepper. Cook, stirring occasionally, until the onion is golden brown, about 15 minutes. Add the radicchio, rosemary and vinegar. Sauté until the radicchio is soft, about 5 minutes. Transfer to the bowl with the pasta.
 
In a small saucepan, warm the milk over low heat. In another saucepan, melt the butter over medium heat. Whisk the flour into the melted butter and continue whisking until it turns light brown, about 2 minutes. Slowly whisk in the warmed milk and bring to a very low simmer. Cook the sauce, stirring often, until it begins to thicken, about 2 minutes. Remove from the heat and season with salt and pepper.
 
Pour the sauce over the pasta and toss to combine. Stir in the Gorgonzola. Taste and adjust the seasoning. Transfer the pasta to a 4-quart (4-l) baking dish and sprinkle evenly with the bread crumbs.
 
Bake until the sauce is bubbling, and the cheese is melted, about 20 minutes. Let cool slightly and serve. Serves 6 to 8.

Adapted from Williams-Sonoma Pasta Night, by Kate McMillan (Weldon Owen, 2014)