Line a baking sheet with foil and place the bacon on it. Bake at 400 degrees Fahrenheit for 18 to 22 minutes or until desired crispness. Keep a close eye on it at the 18 minute mark. Remove from oven and transfer to a paper towel to soak up the grease. Once cooled, chop into bits and set aside.
Boil the pasta according to directions on box, about 7 to 8 minutes. Drain and set aside.
Meanwhile, in a large saucepan, melt butter and flour and cook for one minute. Whisk in milk and stir until mixture thickens slightly. Remove from heat and add the shredded cheese and sour cream. Stir until melted and combined.
Add the cooked macaroni and most of the bacon. Stir, then season with salt and pepper.
Serve with extra chopped bacon and green onions on top.