In a skillet over low heat, add the minced onion and olive oil, then sauté for 10-15 minutes.
When the onion turns golden brown, turn off the heat.
Pour in the tomatoes (whole tomatoes crushed by hand, or canned diced tomatoes) in the skillet and cook over medium heat.
Bring it to a boil, add the bay leaf and salt, then reduce heat to low and simmer it for 7-8 minutes. Turn off the heat.
Once it cools down, blend the sauce in a blender until smooth.