Nettie's Marinara

Heat olive oil in a large saucepan over low heat. Add onions to the pan and sweat the onions low and slow. You're not looking for any browning or caramelization, instead you want them soft and almost melting into the oil. Add salt and stir. Add tomatoes with juices and puree until smooth with an immersion blender. Alternatively, you can puree the mixture in smaller batches using a food processor or blender, then return to the saucepan. Add pepper and basil and simmer for 30 to 40 minutes. The sauce can sit covered while you prepare other add-ins. It keeps in the fridge in a mason jar for up to a week.