Rinse the spinach and blanch in boiling salt water. Drain and rinse in cold water. Finely chop the spinach.
Halve the leek lengthwise, rinse and cut into strips.
Heat the butter in a pan and saute the leek. Mix the spinach, leek, egg, quark and parmesan in a bowl. Season with salt, pepper and nutmeg. Grease a loaf pan with a little butter and pour in the spinach mixture. Bake for about 30 minutes at 180°C (approximately 350°F).
Remove from the oven and cover with aluminum foil. Let rest for about 10 minutes. Cut into slices and serve warm.