Preheat your oven to 350.
Line a cookie sheet (make sure it has a lip) with foil, and top with a cooling rack. I couldn't find a cooling rack, so I just took the grates out of my toaster oven and laid it across the cookie sheet.
Lay the bacon on the rack side by side. Bake for between 15 and 20 minutes.
While the bacon is cooking, you should also boil your pasta. Cook it just under al dente and set that aside.
Now get your bacon out of the oven if it's done to your liking.
Chop it 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. If you want to really go crazy with bacon flavor, you could skip the butter and just use 4 Tbsp of bacon fat at this step. It's up to you :)
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 the shredded cheddar, the salt and pepper, plus 1/2 cup of the chopped bacon. Mix it well until it's nice and smooth. Remove from heat.
Add the pasta to the sauce pan and mix it evenly into the cheese sauce.
Pour into a casserole dish, top with the remaining cup of shredded cheese and the remaining chopped bacon.
Bake for about 30 minutes. Then enjoy!