Put the tomatoes in a roasting tin and toss with 1 tablespoon of the oil until evenly coated, then spread out in a single layer. Roast in a preheated oven, 200°C (400°F), Gas Mark 6, for 20 minutes until soft and lightly charred in places.
Meanwhile, heat the remaining oil in a large, heavy-based frying pan, add the onions and garlic and cook over a medium-high heat for 5 minutes until softened and beginning to turn golden.
Toast the pine nuts in a dry frying pan over a medium heat, shaking the pan occasionally, for 2–3 minutes until golden. Set aside.
Add the rice to the onions and garlic and stir well to coat. Pour in the wine and half the stock and bring to the boil, then simmer gently, stirring, until the liquid is almost all absorbed. Stir in the remaining stock, then simmer gently, stirring frequently, for a further 10–12 minutes until it is almost all absorbed and the rice is tender and cooked through, adding more stock if necessary. Add the basil and cook for 2–3 minutes until wilted, then mix in the pine nuts.
Stir half the roasted tomatoes through the risotto and season well with salt and pepper. Serve in warmed serving bowls topped with the remaining tomatoes.