Pour the tomato sauce into a wide, heavy-bottomed pan
Bring it to a gentle simmer over medium-low heat
Stir frequently to prevent sticking or burning
Cook uncovered to let the water evaporate
Reduce the sauce until it becomes very thick
Lower the heat if it starts splattering
Continue cooking and stirring until it reaches a paste-like consistency
Add a small amount of salt if desired
Let the paste cool completely
Transfer it to a clean airtight container
Store it in the refrigerator or freeze it for later use