Purists often tell you that you shouldn’t add sugar to tomato-based sauces. But that’s fine if you have found the tin of perfect tomatoes, or the ‘ripened-straight-from-the-vine tomatoes’ that can be so expensive at the supermarket.
Often, the fresh tomatoes you buy can be disappointing. They may need to ripen out of the fridge for a few days (it’s best to ripen them in a sunny window rather than store them in the fridge) but you may not have time to do that. When you make a sauce from them, they won’t deliver the sweetness you need. Tinned tomatoes and passata, the puréed tomatoes you buy in a jar, can also be slightly bitter. That’s because the tomatoes are not always picked when they are ripe (you often see a little green or yellow spot on a tinned tomato). To rebalance the bitterness of the tomatoes, it’s perfectly correct to add a little sugar to the sauce.
You can also add a spoon or two of cream to a tomato sauce made with tinned tomatoes at the end of cooking to make a softer tasting, less acidic sauce but only if it suits the recipe.