4-Cheese Mac 'n' Bacon

This is based on a popular dish at T's restaurant in Chicago. But I modified what I tasted and added a touch of bacon to really give it some heartiness. Whoever you serve this to will immediately declare it the best mac 'n' cheese they've ever had. Unite against boxed mac 'n' cheese!

• Ready In: 1 hr
• Serves: 10-12
• Yields: 1 large platter

Ingredients

•  butter, for casserole dish
• 6 -8  slices  thick  center-cut bacon
• 1  medium  white onion, finely chopped
• 1⁄2 cup all-purpose flour
• 5 1⁄2 cups  whole milk (do not use skim)
• 2  teaspoons kosher salt
• 1⁄4 teaspoon fresh ground black pepper
• 1⁄4 teaspoon cayenne pepper
• 1 1⁄2 cups  grated parmesan cheese (about 4 1/2 ounces)
• 1 1⁄2 cups  grated gruyere cheese (about 6 ounces)
• 1 1⁄2 cups  grated Fontina cheese (about 6 ounces)
• 1 1⁄2 cups gorgonzola, broken into small pieces (about 6 ounces)
• 1  lb elbow macaroni

Directions

1. Heat oven at 375 degrees. Butter a 3-quart casserole dish. Fry bacon slices; set on paper towels. Pour off all but approximately 3 tablespoons of the bacon grease. Put pan back on medium heat and add onion. Cook about 5 minutes, until softened. While stirring constantly, add about a third of the flour; continue stirring and slowly adding flour, for at least 1 minute.
2. Transfer onion/flour mixture to a large, heavy saucepan on medium heat. While whisking, slowly pour in milk. Cook while whisking until mixture bubbles and gets thicker (not necessarily "thick"). Remove pan from heat. Add salt, pepper, cayenne pepper, the cheeses and stir. Crumble bacon and add it, stirring. Set aside.
3. Cook pasta in a large saucepan about 2-3 minutes less than box's instructions. Drain pasta in a colander, rinse with cold water, and drain again. Stir pasta into the cooked cheese sauce. Bake until browned on top, about 30 minutes. Let dish stand for at least 5 minutes before serving.