2 russet potatoes, sliced ¼ inch thick
1 (10 oz) package frozen spinach, thawed and drained
1 large yellow onion, diced
1 tablespoon olive oil
½ cup sour cream
½ cup mayonnaise
2 large eggs, beaten
1 teaspoon garlic powder
1 teaspoon kosher salt
½ teaspoon black pepper
1 teaspoon cayenne (optional)
½ cup Parmesan cheese, grated
½ cup Romano cheese, grated
1 cup mozzarella cheese, grated
Preheat oven to 375°F. Coat a 9×13-inch casserole dish with cooking spray. Set aside.
Heat olive oil in a skillet on medium-high heat. Sauté onions until translucent. Transfer onions to a large bowl.
Add spinach to bowl with onions. Add sour cream, mayonnaise, beaten eggs, garlic powder, salt, pepper, cayenne, Parmesan and Romano cheese. Stir until spinach mixture is well combined.
Layer slices of potato in an overlapping pattern on the bottom of the prepared casserole dish.
Pour spinach mixture over top of potatoes. Top with 1 cup mozzarella cheese. Cover with foil and bake for 20 minutes. Remove foil and bake for an additional 15-20 minutes or until cheese on top is golden brown on the edges.
Rest for 5 minutes before serving.