This post shows you how to make tomato purée/paste using fresh tomatoes. Simply stock up on tomatoes while they're in season (or if you grow your own then bonus!) and whip up batched of this tomato puree to last through Winter.
Wash the tomatoes and get rid of the green stems. Then juice the tomatoes (this would yield about 3.5 Litres) *
Sieve the tomato juice into a large saucepan, to get rid of any remaining lumpy bits
Over a low and steady heat begin to reduce the tomato juice mix, stirring every about 20 minutes until you reduce all the water (this process will take several hours) but you can leave them and do other things. When the paste is thick you can switch off the heat, add the salt and leave it to cool down completely.
Place them in a airtight glass jar and top it with the olive oil (thick layer) to make sure it covers the surface to protect the paste (this will seal it and prevent the formation of any mould). Place in the fridge for 3-4 months **
* You are also able to use a blender for the tomatoes, however, this requires a couple of extra steps and it's easier to then boil the tomatoes in water first (or roughly chop and simply fry in a pan to release juices) for 10 minutes to soften before blending. Many also prefer to remove the tomato seeds when making the puree this way as the seeds can make the puree more bitter. ** Alternatively spoon into an ice-cube tray and freeze in individual portions. These can then be kept in the freezer for 8-9 months. 9 pounds of tomatoes yielded about 1.5 cups of tomato paste for me.