Ingredients
at least 1kg/2¼lb fresh tomatoes (less is likely to burn)

Method
1. Wash the tomatoes well in cold water. Cut them in half and remove the white piece in the centre and the seeds; squeeze out any excess water.
2. Remove any hard areas around the tops and stalks of the tomatoes.
Put them into a large casserole dish or stockpot, uncovered, and place them on the hob over a medium heat for 1½-2 hours until soft and broken down into a mushy pulp.
2. Meanwhile, sterilise the jars and lids in a dishwasher or by washing them in very hot soapy water.
3. At the end of the cooking time, pass the pulp through a sieve to extract the skins and some seeds.
4. Using a funnel, pour the passata into the jars leaving a gap of about 2cm/1in at the top.
5. Replace the lids and place into a large preserving pan topped up with water. Make sure the water covers the tops of the jars. Boil for about 20 minutes. You will see the lids become slightly indented at the tops. This is because a vacuum has now been made between the tomatoes and the lid.
6. Remove the jars from the heat and the water and allow to cool before storing in a dark cupboard.