Ingredients:
- 5 lbs Russet or Yukon Gold Potatoes, peeled and quartered
- 4 tbsp Unsalted Butter
- 1/2 cup Whole Milk or Half-and-Half, warmed
- 1/4 cup Grated Parmesan Cheese
- 1 large Egg Yolk
- 1 tsp Kosher Salt
- 1/2 tsp Black Pepper
- 1/2 tsp Garlic Powder
- 1 tbsp Olive Oil
- 1 lb Italian Sausage, casing removed
- 1/2 medium Yellow Onion, finely diced
- 1/2 cup Sliced Mushrooms
- 1/2 cup Sliced Black Olives (pitted)
- 1 tsp Dried Oregano
- 1/2 tsp Dried Basil
- Pinch of Red Pepper Flakes (optional)
- 1 cup Marinara Sauce
- 5 cups Shredded Low-Moisture Mozzarella Cheese
- 1/4 cup Fresh Basil leaves, chiffonaded
Instructions:
- Boil the peeled and quartered potatoes in salted water until fork-tender (about 15-20 minutes). Drain thoroughly.
- Return potatoes to the pot. Mash until smooth. Incorporate the butter, warmed milk, Parmesan, egg yolk, salt, pepper, and garlic powder until a smooth, creamy texture is achieved. Set aside.
- Heat olive oil in a skillet over medium-high heat. Add the sausage and brown, breaking it up well. Drain off any excess grease.
- Add the diced onion and mushrooms to the sausage. Sauté until softened, about 5 minutes.
- Stir in the dried oregano, basil, and red pepper flakes. Cook for 30 seconds until fragrant. Stir in the marinara sauce and black olives. Simmer briefly (2 minutes). Remove from heat.
- Spread the entire pizza filling mixture evenly across the bottom of a prepared 9x13 inch baking dish.
- Carefully spoon the mashed potato mixture over the filling. Use a spatula or the back of a spoon to spread it evenly, sealing the filling completely beneath the potatoes. Create slight peaks and valleys with a fork.
- Sprinkle the shredded mozzarella evenly over the top of the potatoes.
- Bake in a preheated oven at 375°F (190°C) for 30–35 minutes, or until the filling is bubbling hot and the cheese is melted and golden brown.
- Let the casserole rest for 10 minutes before serving. Garnish generously with fresh basil chiffonade.