In a large skillet, heat the oil over medium heat. Saute the onion for 5-7 minutes, till translucent. Add the ground beef and break up with a cooking utensil. Brown the beef. When almost done, add the minced garlic and cook for 1-2 minutes before adding the tomato sauce(or paste and water) and diced tomatoes. Add the bay leaves, italian seasoning and thyme and salt and pepper as desired and bring to a boil. Turn down and simmer till as thick as you'd like it. I like to simmer mine as long as I can, but 20 minutes is enough.
Meanwhile, cook the pasta according to the directions on the package. Drain and set aside. Preheat oven to 400 degrees.
Once the sauce is done cooking, taste for seasonings, adding more salt as needed, and the tablespoon of sugar if needed. In a 9x13 pan, spread a small amount of the sauce along the bottom. Add half the pasta, then half the sauce. Top with the sour cream by dropping small spoonfuls all over the surface and then gently spreading them. Top with half the cheese. Add the rest of the pasta, then the rest of the sauce and finally the rest of the mozzarella cheese.
Place in the oven to bake for 35-40 minutes until the sauce can be seen bubbling. Broil so that the top gets golden if desired, then let cool for a few minutes before serving alongside a green salad.