2slicesAmerican Cheese or 1 tablespoon of Velveeta CheeseOptional. This is added to help keep the cheese from splitting, but not necessary. If you omit, there will be some oil that separates out of the cheeses - this is normal.
The day before making the casserole, bake the potatoes at 400°F for 45 - 55 minutes until completely cooked through. Cool on the countertop and then chill in the fridge overnight.
Cream of Bacon Soup
Add the heavy cream, milk, chicken stock, bay leaf, onion powder, granulated garlic, kosher salt, black pepper, and corn starch to a cold, medium saucepan, stirring to incorporate. Turn heat to medium-high and bring to a boil, stirring frequently. Reduce heat to medium, and simmer for 5 to 8 minutes until thickened.
Remove from heat and add in bacon fat and allow to cool slightly.
This can be made ahead of time and stored in the fridge for several days until needed.
Assembly
Preheat oven to 350°F
While the oven is preheating, grate the chilled potatoes with the large holes of a cheese grater and add to a large mixing bowl.
Fold in the prepared Cream of Bacon Soup, diced onion, ¾ of both Colby and Gouda cheeses, American cheese (if using), sour cream, melted butter, and salt and pepper.
Pour mixture into a 9x13-inch casserole dish, and top with remaining Colby and Gouda.
Bake for 55 - 60 minutes until bubbly and brown.
Optimally, broil on high until browned to your liking.