Bring a large saucepan of lightly salted water to a boil. Cook spaghetti in boiling water for 8 to 10 minutes or until al dente; drain. Preheat oven to 180 degrees C.
In a 2 litre casserole dish whisk together egg, milk and sour cream. Using a wooden spoon stir in spinach, artichoke hearts, cheese, 2 tablespoons Parmesan cheese and cooked spaghetti. Season with dried onion, salt and pepper. Top with a sprinkling of paprika and remaining Parmesan cheese.
Cover and bake in preheated oven for 15 minutes. Remove cover and bake for another 15 minutes. Let stand 2 minutes before serving.