1. Place the potatoes in a large saucepan of salted water and cover. Bring to a boil, then simmer for 30 minutes, until just tender. Drain, cool, and peel. Shred the potatoes into a bowl.

2. Heat the butter in a frying pan over medium heat. Add the onion and fennel and cook until tender, about 10 minutes. Transfer to a bowl. Add the potatoes, eggs, flour, and nutmeg, and season with salt and pepper. Mix well.

3. Preheat the oven to 200°F (95°C). Heat 3 tbsp of oil in a large nonstick frying pan over medium-high heat. In batches, add about ¼ cup of the potato mixture for each pancake, and flatten with a spatula. Cook, turning once, about 7 minutes, until golden. Keep warm in the oven while making the remaining pancakes.

4. Heat the remaining oil in the frying pan over medium-high heat. Add the mushrooms and garlic and cook about 5 minutes until the mushrooms are browned. Stir in the thyme and lemon juice, and season with salt and pepper.

5. Serve the pancakes, topped with the mushrooms, Parmesan shavings, and a dollop of créme fraîche.