Peel and finely chop the onion, garlic and carrots along with the celery – they don't have to be too fine if you are going to blend the sauce later.
Heat the oil in a heavy-based pan, add the onion, carrots, celery and garlic and cook gently for about 10 minutes until soft.
Add the chopped tomatoes, tomato purée, sugar and rosemary or paprika. Cook for about 10 minutes, until the sauce has thickened slightly.
You have the choice to leave the sauce chunky with bits of carrot, celery and onion or you can give the sauce a quick whizz with a handheld blender or food processor until smooth.
Add the beans to the sauce and cook for another 10 minutes until heated through.
Cook's tip: for little ones, you can squash the beans and mix with mashed potato or baby rice.