Is there anything that will make a tart spaghetti sauce sweeter?

Yes, here are a few things that will make a tart spaghetti sauce sweeter:

- Sugar: Adding a small amount of sugar can help to balance the acidity of the sauce and make it sweeter. Granulated sugar, brown sugar, or honey can all be used for this purpose.

- Sweeteners: Natural sweeteners like maple syrup, agave syrup, or molasses can also be used to add sweetness.

- Caramelized onions: Caramelizing onions in olive oil until they are soft and sweet will add sweetness and depth of flavor to the sauce.

- Roasted vegetables: Roasting vegetables like carrots, red peppers, or sweet potatoes and adding them to the sauce can also help to balance acidity and add natural sweetness.

- Dried fruit: Adding a small amount of dried fruit like raisins, currants, or cranberries can provide a sweet and tangy flavor to the sauce.

- Fresh herbs: Adding fresh herbs like basil, oregano, or thyme can help to balance the acidity of the sauce. These herbs can be added at the end of cooking to ensure they do not lose their flavor.