Fill a pot with water. Add the whole onion, carrot, and celery. Season with salt and simmer gently for 30 minutes.
Prepare the Tomato Sauce
Peel the garlic. Sauté it whole in olive oil until golden, then remove. Add tomatoes and basil leaves, season with salt, and simmer on low for 15 minutes.
Start the Risotto
Start your tomato risotto by toasting the rice in a warm pot with a little fat, stirring constantly. Deglaze with white wine and let it reduce.
Add Broth Gradually
Begin adding hot broth gradually, stirring throughout.
Add Tomato Sauce
About halfway through the cooking time, add the tomato sauce. Depending on the rice variety, total cooking time is about 15–20 minutes.
Finish with Mantecatura
Once the rice is al dente, remove from the heat and stir in butter and cheese. Garnish the tomato and basil risotto with fresh basil just before serving.