Heat oven to 350 degrees. Mist a 9- by 5-inch loaf pan with non-stick cooking spray and set pan aside.
In a large skillet, cook spinach and 1 tablespoon water over medium-high heat, tossing occasionally until spinach is wilted. This will take only 3 or 4 minutes. Remove from heat and set pan aside.
In a large bowl, beat eggs and stir in sour cream, onion, Parmesan cheese, flour, melted butter, pepper and nutmeg. Add cooked spinach and mix well. Pour mixture into prepared pan and bake, uncovered, for 35 minutes. Remove from oven, cool for 5 minutes, and cut into rectangles to serve.