Heat olive oil in a large saute pan over medium-high heat. Add the sausage, break apart and crumble with a spoon, and cook until browned.Using a slotted spoon, remove sausage from the pan and transfer to a large mixing bowl. Set aside.
Add onion, red pepper, and potatoes to the sauté pan, and sauté for 5 minutes, softening the onion and red pepper and lightly cooking the potatoes. Then add the garlic and sauté for an additional 2 minutes until softened. Add this vegetable mixture into the mixing bowl with the sausage. Add 1 ½ cups cheese to the mixing bowl with the sausage and veggies. Stir to combine.
In a separate bowl, whisk together the eggs, milk, and black pepper. Then add this egg mixture to the bowl with the hashbrown mixture, and stir to combine. Carefully pour the combined ingredients into a 9×13-inch baking dish. Top with the remaining ½ cup of shredded cheese. Cover with aluminum foil and refrigerate overnight.
In the morning, remove from the refrigerator and let sit for a few minutes at room temperature while you preheat the oven to 375°F.
Cover with foil and bake for 30 minutes. Remove the aluminum foil and bake for an additional 15-20 minutes, until the potatoes are cooked through.
Remove and let the casserole rest for 5 minutes. Garnish with parsley or green onions and serve immediately.
Notes
DAIRY-FREE OPTIONS: This recipe can easily be made with your favorite dairy-free milk alternative (I use almond milk) and dairy-free shredded cheese (I use this dairy-free brand).