Pre-heat the oven to 200°C (fan)/220°C/gas mark 6*.
Put the 1 kg chopped potatoes into a large saucepan and cover with water. Bring to the boil and parboil until just starting to turn soft.
Heat the remaining olive oil in a medium saucepan. Add 1 chopped onion and sauté over a low heat for around 10 minutes until soft. Add 2 cloves chopped garlic, stir and cook for a few minutes.
Now add a 400g tin of chopped tomatoes, 1 tbsp tomato pureé, 1 tsp smoked paprika, 1 tsp dried oregano, 1 tbsp balsamic vinegar and the chilli flakes if using. Stir well and bring to the boil.
Reduce the heat and simmer gently for up to 45 minutes until the sauce has thickened. Making this in advance will only be a good thing for the sauce. Season with salt and pepper to taste.
If serving to children who object to onions you could blend the sauce at this stage.
*If you prefer you can use boiled potatoes for this dish.
** You can leave the potatoes unpeeled if you prefer.