Heat olive oil in a medium saucepan over medium high heat. Add onion and cook until softened (stirring frequently), about 3 minutes.
Add garlic and cook an additional 30 seconds, stirring constantly.
Add crushed tomatoes with juices, tomato paste, oregano, red pepper flakes, salt, pepper and bay leaf. Stir to combine.
Bring to a simmer and reduce heat as necessary to maintain a simmer (medium low to low).
Cover and simmer for 20 minutes, stirring about 3 times during simmering. *Exercise caution when removing lid to stir - the sauce tends to splatter while simmering. Stir about 3 times (every 6 to 7 minutes) during simmering to prevent sticking to the bottom of the pan.
Remove from heat. Remove bay leaf and discard. Stir in fresh basil.