Blitz the tomatoes using a jug or stick blender, in batches if necessary, until you have a coarse purée, in batches if necessary. Add all the remaining ingredients except the sugar and blend until well combined.

Pour the blended mix into a non-reactive cooking pot and add the sugar. Bring to a gentle simmer and cook over a low heat until reduced to a thick consistency; this should take about 30 minutes.

Note: Pot the jam you aren't using immediately into a warm sterilised jar while still hot and secure with a lid. Store in a cool dark place for up to 6 months. Once opened, keep refrigerated and use within a month.