01 -
Preheat oven to 356°F (180°C).
02 -
Bring a large saucepan of water to a boil, add the sliced potatoes, and cook for 10 minutes until just tender. Drain well.
03 -
In a large skillet, heat the olive oil and butter over medium heat. Add the red onion, garlic, and green onions; sauté until softened. Stir in the drained spinach and cook for 5 minutes. Season with nutmeg, salt, and black pepper.
04 -
In a separate pan, heat sunflower oil over medium heat. Whisk in the flour and cook for 1 minute. Gradually pour in water and milk, whisking constantly, until the sauce thickens, about 5 minutes. Adjust seasoning with salt, black pepper, and nutmeg.
05 -
Grease a deep baking dish with a small amount of oil or butter. Layer half of the potato slices on the bottom, followed by half the spinach mixture and then half of the white sauce. Repeat the layers with remaining ingredients.
06 -
Sprinkle the grated mozzarella cheese evenly over the top layer.
07 -
Bake in preheated oven for 30 to 35 minutes, or until the cheese is golden and bubbling. Remove from oven and allow to rest for 5 minutes before serving.