Oven 220c.
Prepare the ingredients. Drizzle 1 tbsp oil onto a large baking tray and spread this about with a pastry brush or clean hands. Tip the potatoes on the tray and drizzle over 1 tbsp oil. Mix them around with your hands to ensure they are covered with the oil. Spread out, making sure they don’t touch, otherwise they won’t crisp up. Bake for 30 - 40 mins, turning the potatoes over half way through cooking.
Add the other 1 tbsp oil to the pan and heat. Throw in the onions, stir and cover, then lower the heat to medium. Stir occasionally until starting to soften. Don’t be tempted to turn up the heat as you don’t want them to brown..
Add the paprika, chilli flakes, garlic and stir well for a few minutes. Pour the tomatoes in the pan, add the vinegar if using, then stir, cover and cook on a medium heat for 15 mins. You can either leave the sauce chunky or blend as I have here (brilliant to disguise onions to the most discerning little one!)
Once the potatoes are browned and cooked through, remove and tip into a serving dish. Season well with salt and pepper then spoon over the sauce. An remaining sauce can be served on the side. Scatter with the parsley or oregano if using, and serve.