I set myself to make the Sofficini today.
I have had the tomato sauce prepared a while ago. I am against buying what you can easily prepare yourself. I also had some very ripe tomatoes.
Not to mention a basic tomato sauce could always come in handy in a wide range of recipes.
Here is how I make it: I brown diced onions and crushed garlic then when they get a golden color, I add the cored and peeled tomatoes and season with salt and pepper. Some add some sugar but I prefer the acidity of tomatoes, so it is a matter of taste. Then I let it simmer till it becomes a little less thick than a paste and blend when cold.