Place a saucepan over medium heat. Add olive oil and let it warm gently until it shimmers slightly around the edges.

Add chopped onion to the pan. Stir slowly and cook until soft and clear, which releases sweetness and builds deep flavor.

Add minced garlic and cook briefly. Stir for thirty seconds so it softens but does not burn, because burnt garlic tastes bitter.

Pour in the crushed tomatoes. Stir well to mix with onion and garlic and scrape any browned bits from the bottom for flavor.

Add salt, pepper, oregano and red pepper flakes if using. Stir gently so spices spread evenly and begin flavoring the sauce.

Reduce heat to low and let sauce simmer for about twenty minutes. Stir sometimes so it does not stick and cooks evenly without burning.

Tear fresh basil leaves and stir in. Taste the sauce and add sugar if tomatoes are very acidic, or water if it feels too thick.

Turn off heat and let the sauce sit for a few minutes. Resting allows flavors to blend smoothly, giving rich and balanced taste.