Step 1

Preheat oven to 350 degrees F. Cook macaroni for half the time of the package instructions, drain, and set aside.

Step 2

In a large skillet, fry the bacon until crispy. Drain on a paper towel, and chop into small bits. Reserve 1 tablespoon of the bacon grease.

Step 3

In the same skillet that you fried the bacon in, add the onions, and cook over medium-low heat for 15 to 20 minutes, or until golden-brown, caramelized, and soft. Set aside.

Step 4

In a pot, melt 4 tablespoons butter. Sprinkle in flour, and whisk to combine. Cook, stirring constantly, over medium heat for 1 minute.

Step 5

Pour in milk, and cook for 3 to 5 minutes, or until thick. Reduce heat to low. Add salt and pepper to taste. (Do not under-salt!)

Step 6

Beat egg yolks in a separate small bowl, and then drizzle 1/4 cup hot milk mixture into the yolks, stirring constantly. Pour egg mixture back into sauce, and cook for another minute.

Step 7

Add cheese, and stir until melted. Add onions and bacon, and stir. Taste for seasoning, and add more salt if needed.

Step 8

Add cooked macaroni and stir to coat.  Pour into a baking dish, and bake for 15 to 20 minutes, or until sizzling and hot.