Wash and core tomatoes
Cut tomatoes into quarters
Steam or simmer tomatoes until soft (about 20–40 minutes)
Blend or mash tomatoes to a smooth puree
Strain puree through a fine sieve or cheesecloth to remove seeds and skins (optional)
Simmer strained puree in a wide pot until thick (about 1–3 hours), stirring often to prevent scorching
Spread thick puree on a parchment-lined baking sheet (optional for faster reduction)
Bake at 200°F / 95°C, stirring every 20–30 minutes until very thick (optional)
Reduce to desired thickness for paste
Taste and adjust with salt only if desired (optional)
Cool completely
Store in airtight containers
Refrigerate up to 1–2 weeks
Freeze for longer storage (portion into small containers or ice cube trays)