Wash ripe tomatoes
Remove stems and any damaged parts
Cut tomatoes into chunks
Cook tomatoes in a large pot over medium heat
Stir occasionally until tomatoes soften and release juice
Blend or mash the cooked tomatoes until smooth
Strain through a sieve or food mill to remove skins and seeds
Return the strained puree to the pot
Simmer on low heat, stirring often, until thickened
Continue cooking until it reaches a paste-like consistency
Add salt if desired
Cool completely
Store in a clean airtight container in the refrigerator or freezer