Instructions

• 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.