Preheat oven to 350 degrees.
Brown your hamburger in a large pan over medium heat, breaking into small pieces. Drain.
Add tomato sauce and paste, salt and pepper, water (with the bouillon cubes in it), sugar, basil, oregano and garlic. Simmer on low for 10 minutes.
While sauce is simmering, cook the spaghetti noodles as directed on the package, and set aside.
Add 1 cup sour cream and 1 cup mozzarella cheese to the sauce and stir to combine. Add noodles and mix well.
Pour spaghetti mixture into a greased 11 x 14 baking dish and sprinkle with 1 cup shredded mozzarella cheese.
Cover the casserole with foil and bake for 25 minutes, then remove the foil and bake for an additional 5 - 10 minutes, until the cheese is melted.