Heat oil in a deep sauce pan or Dutch oven on medium heat.
Reduce heat to medium-low and cook onion with a pinch of salt for 5 minutes. Add garlic, oregano (if using) and chili flakes and continue to cook for 1 minute just until the garlic starts to sizzle.
Turn heat to low, stir in red wine and let simmer for 2-3 minutes. Turn heat back up to medium and add tomatoes. Set timer for 15 minutes and, once the sauce starts to bubble, return heat to medium-low and let simmer until reduced.
Remove from heat and season with more salt to taste (I like to add about ¼ teaspoon at this point).
Next, remove from heat, add basil leaves and purée until smooth (either a food processor or immersion blender will work). Serve immediately or let cool completely before transferring to storage container(s).