1Puree boiled potatoes in a wide bowl. Add egg, milk, salt, black pepper and butter. Transfer into a Pyrex Dish.
Meanwhile, sauté onion with olive oil and stir in garlic. After a while add spinach and cook for 4-5 minutes over medium heat. Spread it over potato puree. Sprinkle cheese all over.
Bake at 400 F (200 C) oven, till the top gets lightly brown (for about 20-25 minutes). Serve warm.