2 tablespoons (1/4 stick) butter
1/4 cup all purpose flour
2 cups whole milk
1 cup whipping cream
3 cups grated cheddar cheese
1 1/2 cups crumbled blue cheese
1 tablespoon minced fresh chives
Preheat oven to 350F. Butter 13x9x2-inch glass baking dish. Cook
pasta in large pot of boiling salted water until tender but still
firm to bite, stirring occasionally, about 8 minutes. Drain.
Meanwhile, melt butter in heavy large saucepan over medium-low heat.
Add flour. Cook 1 minute, stirring constantly (do not allow to
brown). Gradually whisk in milk and cream. Simmer until mixture
thickens slightly, whisking occasionally, about 3 minutes. Reduce
heat to low. Add grated cheddar cheese and 1 cup crumbled blue
cheese. Whisk until cheese melts, about 2 minutes. Season sauce to
taste with salt and pepper.
Add cooked pasta to sauce; stir to coat. Transfer mixture to
prepared baking dish. Sprinkle with remaining 1/2 cup blue cheese.
Bake until sauce begins to bubble, about 25 minutes. Sprinkle with
chives and serve.