Bring a large pot of water to boil, score an X at the bottom of the tomatoes and toss them in the boiling water until the peel starts coming off (a couple of minutes).
Drain them with a skimmer and move them to a bowl of ice-cold water. You can then use the same boiling water for the vegetable stock.
Remove the peel of the tomatoes and toss them in a blender. Blend until you get a smooth sauce.
Finely chop the onion and add it to a large pan with a knob of butter. Add the rice and sauté at medium heat for a couple of minutes to toast the rice. Make sure to not burn the rice nor the onion.
Add the white wine and let it evaporate completely. Then add a couple of ladles of vegetable stock. Once the rice starts to absorb it, add the tomato sauce and the basil leaves.
Stir well and let it cook until the rice is al dente, adding more stock if it becomes too dense. When the rice is cooked, turn off the heat and add the butter. Mix well to incorporate while it melts, then serve immediately. You can add some freshly grated Parmigiano on top.
Notes
Store leftovers in an airtight container in the fridge for up to 3 days. Reheat gently on the stove over low heat, adding a splash of broth or water to loosen the risotto and restore its creamy texture. Avoid microwaving if possible to preserve the best texture.