Preheat oven to 350°F. Lightly grease a 9x13-inch casserole dish with Tillamook butter.
Cook the sausage, breaking into small pieces, until browned. Remove from pan and add to casserole dish.
Add the onion and red bell pepper to pan. Cook until softened, about 5 minutes. Transfer the mixture to the baking dish, add the potatoes, and combine.
Whisk together the eggs, Tillamook sour cream, ½ and ½, mustard, cheese, salt, and pepper. Pour over the mixture in the casserole dish and finish with remaining ½ cup of shredded cheese
Bake about 45 minutes or until egg custard is set.
