Bring a large pot 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 350 degrees F (175 degrees C).
In a 2 quart casserole dish, whisk together egg, milk, and sour cream. Using a wooden spoon, stir in spinach, artichoke hearts, Monterey Jack cheese, 2 tablespoons Parmesan cheese, and cooked spaghetti. Season with minced 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.