Begin by grating 600 g of starchy potatoes into a large bowl. Soak the grated potatoes in cold water with a pinch of salt for 15 minutes to draw out excess starch. Once soaked, drain them well and use your hands to squeeze out any remaining moisture.

In a skillet, heat 2 tablespoons of olive oil over medium heat. Add one chopped green onion and sauté for 2-3 minutes until softened. Toss in 150 g of baby spinach, stirring until it wilts, then incorporate 200 g of chopped champignon mushrooms, seasoning with salt, pepper, and 2 teaspoons of dried oregano. Cook until the mushrooms turn golden, about 8 minutes, and set aside to cool.

In a large mixing bowl, combine the drained grated potatoes, 80 g of mozzarella cheese, and 2 large eggs. Stir in 2 tablespoons of freshly chopped parsley, along with salt, pepper, and 2 teaspoons of oregano. Mix thoroughly until all ingredients are well combined.

Preheat your oven to 200°C (390°F). Lightly brush a springform pan with 2 tablespoons of olive oil to prevent sticking. Press the potato mixture firmly into the bottom and up the sides of the pan to create a high crust.

Place the crust in the preheated oven and bake for 35-40 minutes until golden and crispy. After baking, remove it from the oven and allow it to cool slightly.

Spoon the cooled mushroom-spinach mixture into the potato crust, spreading evenly. Top it off with the remaining mozzarella cheese (100 g), 120 g of mozzarella fior di latte, and 30 g of grated Parmesan. Return the pie to the oven and bake for an additional 10-15 minutes until the cheese is melted and bubbling.

After the final bake, remove the Crispy Grated Potato Pie from the oven and let it cool for 5 minutes. Garnish with fresh parsley, slice, and serve warm.