Cut the potatoes into 2cm dice, and toss with some oil and plenty of salt and pepper. Spread in a single layer on a baking tray, and roast for around 45 minutes at 190°C (Gas Mark 5 / 375°F), or until the potatoes are soft in the middle and crispy on the outside.
While the potatoes are roasting, make the tomato sauce. Add all of the sauce ingredients to a blender, and blend until smooth. Transfer the mixture to a pan, and place over a medium heat. Bring to a gentle simmer, and cook for around 15 minutes, until the mixture has thickened to your desired consistency.
To make the garlic aioli, add the garlic to a mini food processor with the fresh parsley. Blitz until finely chopped. Add the mayonnaise and a dash of milk, and blitz again.
When the potatoes are cooked, serve them topped with the tomato sauce and garlic aioli.