Preheat the oven to 275 degrees F.
Place a large roasting pan over 2 burners set to medium heat. Add the butter, garlic and onions and sweat for 6 to 7 minutes. Add the tomato paste and cook for 2 to 3 minutes more. Add the tomato sauce and chicken stock and bring to a simmer. Cover with foil and transfer the pan to the oven for 5 hours, stirring every 30 minutes. (Baking in the oven ensures the sauce cooks down without burning.)
Transfer the sauce to a blender along with the basil, Parmesan and sugar, and blend well. Season with salt and pepper. Toss the cooked pasta with the sauce. Serve in shallow bowls, garnished with Parmesan.