Heat olive oil and butter in a medium saucepan, over medium-low heat. Add the minced garlic, oregano, crushed red pepper, and salt, and stir frequently until you begin to smell the garlic and herbs (2-3 minutes).
Add the tomatoes, tomato paste, onions, basil, and sugar, and puree using a hand blender, until smooth. (You can also use a food processor for this step.)
Return the sauce to the stove over medium heat. Once the tomatoes begin to simmer, reduce the heat to the lowest setting, where the sauce just bubbles lightly. Cook for 1 hour, until the sauce has reached your desired consistency.
Taste the sauce and add additional salt, if desired.
Use immediately, or cool and store refrigerated in an airtight container for up to 2 weeks.