Preheat your oven to 350 degrees.
Line a cookie sheet (with a lip/high edges) with foil, and top with a cooling rack if you have one. (This keeps bacon separate from grease)
Lay the bacon on the rack side by side. Bake for between 15 and 20 minutes.
While the bacon is cooking, boil your pasta. Cook it just under al dente and set that aside.
Get your bacon out of the oven if it's done to your liking.
Chop the bacon up and set it aside for later - but keep that bacon fat! Pour it in a jar.
In a large sauce pan, melt 2 Tbsp of butter with 2 Tbsp of the bacon fat over medium heat. Or swap the butter for 4 Tbsp of bacon fat for more bacon flavor.
Once the butter has melted and mixed with the bacon fat, add the chopped green onions. Mix them up for a few minutes to soften them.
Add the flour and whisk like crazy until it's well blended.
Add the milk. Slowly heat while whisking until is starts to bubble.
Add 3 cups of shredded cheddar, salt, pepper, and 1/2 cup of the chopped bacon. Mix it well until it's nice and smooth. Remove the pan from heat.
Add the pasta to the pan and mix it evenly into the cheese sauce.
Pour into a baking dish, top with the remaining cup of shredded cheese and the remaining chopped bacon.
Bake for about 30 minutes. Then enjoy!