Plunge fresh tomatoes into boiling water for 30 seconds, then peel and crush (if using canned tomatoes, skip this step).Heat the olive oil in a frying pan over medium heat. Add finely chopped onion and garlic and sauté until translucent.Add the crushed tomatoes, a pinch of sugar (optional), salt and pepper. Simmer over low heat for 15 minutes, until the sauce thickens.Add torn basil leaves at the end of cooking. Set aside.