1. Thaw the artichoke hearts.
2. Chop the spinach, rinse with cold water, drain and cut into strips. Cook in a pan with 2 tbsp of butter. Add salt and pepper. Add the artichokes, 2 tbsp of butter, 3 tbsp of water, salt, and pepper. Cook covered for 10 minutes over medium heat.
3. In a small saucepan, melt 2 tbsp of butter, add the flour, and cook for 2 minutes. Add the milk and bring to a boil. Remove from heat. Season with salt, pepper, and nutmeg. Mix well and cook again over low heat for 10 minutes.
4. Remove the saucepan from the heat and, stirring, add the spinach and artichokes.
5. Meanwhile, cook the pasta in a large quantity of salted water. Drain and plunge into cold water for a few seconds; drain again and put the pasta on a kitchen towel.
6. Brush a baking dish with the remaining melted butter. Arrange the pasta, alternating with the spinach and artichoke mixture and parmesan.
7. Spread the spinach and artichoke mixture over the top layer; finish with parmesan.
8. Bake for 10 minutes at 350°F, until golden brown, and serve immediately.