Begin by grating 600 grams of starchy potatoes using a box grater. Soak the grated potatoes in a large bowl of cold salted water for 15 minutes to help remove excess starch.

In a skillet, heat 2 tablespoons of olive oil over medium heat. Add one chopped green onion and sauté for about 2 minutes until softened. Then, add 150 grams of baby spinach and cook until wilted for about 2-3 minutes, followed by 200 grams of sliced champignon mushrooms seasoned with salt and pepper. Cook for another 6-8 minutes until golden.

In a mixing bowl, combine the drained grated potatoes with 80 grams of mozzarella cheese, 2 large eggs, 2 tablespoons of chopped parsley, 1 teaspoon of dried oregano, and a pinch of salt and pepper. Mix thoroughly.

Preheat your oven to 200°C (390°F). Grease a baking dish with 2 tablespoons of olive oil. Press the potato mixture into the dish, creating a crust about 2 inches high. Bake for 35-40 minutes until golden and crispy.

Once the crust is baked, remove it from the oven. Spoon in the sautéed mushroom and spinach mixture evenly. Top with remaining mozzarella, 120 grams of fior di latte, and 30 grams of Parmesan cheese.

Return the pie to the oven for another 10-15 minutes until the cheese is melted and bubbly. Watch closely until slightly golden.

Let the pie cool for about 5 minutes to set the layers. Garnish with fresh parsley, slice into wedges, and serve.