Preheat the oven to 200°C/390°F/Gas Mark 6. OR instead of roasting the potatoes you can parboil them for 7 minutes, drain and then fry until crisp and golden (either way works well)
If roasting, place the potatoes on a baking tray with a little oil and salt and pop in the oven for 40 minutes (or until crisp and golden), turning once
While the potatoes are cooking, fry the onion in a small amount of olive oil until soft and golden
Add the chilli and garlic and fry for a further minute
Now stir through the tinned tomatoes, sugar, salt, smoked paprika. Bring to the boil and simmer for 15-20 minutes or until the mixture is thicker and has reduced down
Stir in the vinegar and then taste the sauce, adjusting the seasoning if necessary