It’s easy. Take a ridiculously large amount of perfectly ripe Sicilian tomatoes. Cut them up. Leave them in the sun for 4 days to reduce down to about one-tenth of their original volume.
Making tomato paste, called stratto, is a summer tradition in Sicily. It requires good weather and slightly inclined wooden boards that absorb and drain the liquid, readying the preserves for their storage in a cool, dry place until winter. 
