Preheat oven to 400 degrees.
Line a sheet pan with parchment paper, then place a wire rack onto the sheet pan. Place the strips of thick-cut bacon on the wire rack, make sure the bacon is laying flat and the pieces of bacon do not overlap.
Place the sheet pan on the center rack of the preheated 400-degrees oven.
Cook the bacon until it is crispy in 18-20 minutes.
Reduce oven temperature to 350 degrees to bake the dressing.
Remove the bacon after it is crispy. Transfer the bacon to a plate or bowl lined with paper towels. Reserve a tablespoon of bacon drippings.
Place a skillet over med-high heat and add a single tablespoon of extra virgin olive oil.
When the oil is hot, add the Italian sausage, break it apart with a spoon, brown the sausage, and then transfer it onto a plate or bowl lined with paper towels.
Wipe the skillet clean, place it over medium/high heat, and toast the walnuts for 1-2 minutes. Transfer the walnuts to a small bowl and set aside.
Add the tablespoon of bacon drippings to the skillet and place it over medium/high heat.
When the pan is hot, add the onions, apples, celery, and red and green bell peppers, and sauté for five minutes. Remove the mixture from the skillet into a bowl and set aside.
Add 2 1/2 cups of the sourdough cubes and 3 cups of the crumbled cornbread into a large bowl. Fold in the crumbled thick-cut bacon, Italian sausage, onions, apples, celery, red and green bell peppers mixture, toasted walnuts, and chopped flat-leaf parsley, and add in the seasonings.
Gently fold all ingredients together, and add the chicken stock one cup at a time. Fold the mixture after you add each cup of chicken stock. The key to great dressing, it shouldn't be soggy or too dry. However, adjust to your preference. I like my dressing to be moist; it will lose a bit of its moisture while cooking in the oven. After mixing the ingredients, give it a taste and adjust the seasoning. You won't need to add salt because you will get salt from the thick-cut bacon and Italian sausage.
Spoon the dressing into your preferred baking dish; this should be a high-walled dish about 2 to 4 inches deep.
Cut pieces of the half-stick of unsalted butter all over the top of your dressing. I always make sure to tuck a few pieces into the corners.
Place the dressing onto the center rack of a preheated 350-degree oven and cook for an hour.
Remove from the oven and serve with cranberry sauce, turkey, or sausage gravy.