Begin by preheating the oven to 200°C/400°F/Gas Mark 6.
Place the potatoes in a roasting tin and coat with 2tbsp olive oil. Roast them in the centre of the oven for 20 mins.
Remove from the oven and add the rest of the ingredients, drizzling over the remaining olive oil and grinding over some black pepper. Return to the oven for 20-25 mins, or until the potatoes are tender and the skins on the tomatoes are just starting to split. Serve immediately.
Notes
The way to tell whether a potato is new – rather than just small – is to rub the skin. It should come off easily.