In a large saucepan over medium-high heat, melt the butter. Add the onion and cook, stirring, for about 3-5 minutes (or until soft). Add the garlic and cook, stirring, for 1 more minute.
Stir in the tomatoes and reduce heat to medium low. Add basil, oregano, sugar, salt and pepper.
Simmer, partially covered, stirring regularly, until sauce is thickened (about 10-15 minutes).
Taste the sauce, and add additional salt, pepper and herbs if desired.
If using fresh tomatoes, use a handheld stick blender, a food processor, or a large blender to puree the sauce until smooth. If using canned crushed tomatoes, you can skip this step.