Cook the pasta to al dente according to package directions.
While the pasta cooks, fry the bacon in a large cast-iron (or other oven-safe) skillet until crispy.
Remove the bacon and place it on a plate lined with paper towels to drain. Wipe out the pan.
Add the sausage.
With your spatula, break it up and cook for a few minutes.
Once cooked, remove from the pan and set aside.
Preheat your oven to 375°F.
Melt the butter in a skillet. Add the shallots along with a sprinkle of salt. Sauté for a few minutes until softened. Next, add in the garlic.
Stir in the flour until your mixture becomes a pasty roux.
Over low-medium heat, gradually pour in the milk as you whisk the mixture. Continue to whisk until the mixture has significantly thickened.
Now whisk in the sour cream, being sure to completely blend.
Remove the skillet from the heat. Next, add 3 cups of cheddar cheese. Stir the mixture until the cheese is completely melted and incorporated.
Add the elbow pasta to the skillet. Stir to coat the pasta well.
Crumble the bacon and stir half of the crumbles into the macaroni.
Using a skillet or small saucepan, melt the remaining three tablespoons of butter on medium heat.
Now add your Italian breadcrumbs and garlic salt. Be sure to stir until toasted and golden brown.
For finishing touches, top the elbow macaroni with the remaining cheese and bacon as well as the Italian breadcrumbs.
Bake your masterpiece for 15 minutes. You will see that the mixture is bubbly and crispy on its edges.
Garnish with chopped green onion or parsley before serving.