Add a small amount of sugar
Add grated carrot or finely diced onion
Simmer longer to mellow the acidity
Add a pinch of baking soda
Use ripe, low-acid tomatoes
Add dairy such as butter, cream, or milk
Add olive oil
Add a pinch of salt
Balance with sweet vegetables like bell peppers
Use less tomato paste
Add a small amount of honey
Serve with cheese or a creamy topping