Wash and remove any bad spots from your tomatoes. You do not need to peel or core them since they will be thoroughly blended before you are done. Put your quartered tomatoes, onion, red pepper, vinegar and 1/2 tablespoon salt into a large pot over a medium-high flame. Bring to a boil and then simmer for 40 minutes, or until all of the vegetables are very soft.
Using your stick blender carefully puree the sauce until it is very smooth. This can also be done in batches in your blender, being extremely careful since hot stuff expands. Be sure the lid is covered with a towel you hold over it and the center feed cap is removed to help prevent burns. However you do it, make the sauce as smooth as you would like it to be before proceeding.