Heat the oil in a medium saucepan over medium heat. Put the onion and garlic, and saute until softened. Add the carrot and celery, and saute for 5 minutes.
Add the tomatoes and sugar, and bring to the boil. Decrease the heat to low and gently simmer for 45 minutes. Remove from the heat.
Pour into a food processor and blend until pureed. Return to the pan and stir in the basil. Return to the heat and bring to the boil. Season with salt and pepper and gently simmer over low-medium heat for a further 5 minutes.
This is good for all types of pasta especially in potato gnocchi.
