Cook pasta according to package directions. Drain, reserving 1 cup of pasta water.Heat butter and oil over medium heat. Add onions and garlic and saute for a minute or so. Pour in tomato sauce and add salt, pepper, and sugar to taste. Stir and cook over low heat for 25 to 30 minutes, stirring occasionally.Remove from heat and stir in cream. Add cheese to taste, then check seasonings. Stir in pasta and chopped basil and serve immediately. (Thin with pasta water before adding basil if needed.)