Heat the olive oil over a medium heat in a large heavy base pan. Add the tomatoes can cover.

Every 5 minutes gently stir/turn the tomatoes to let all of them get to the heat. Do this for 15 minutes.

Add the garlic and chillis whole and season well. Cover again and cook on medium heat for a further 15 minutes, again stirring every 5 minutes.

Uncover and lower the heat, simmer for 1-2 hours.

Taste and season, you can add tomato puree if you want to thicken it.

Allow to cool and freeze in bags.