This soup is rich, savory, with a hint of sweetness; not to mention a bit of tang from a surprise ingredient: buttermilk!
Using sauté setting – begin melting butter and add onions. Cook onions for about 3 minutes, stirring frequently. You don’t want any color on them, so if they begin to brown, turn off heat.
Add diced tomatoes, tomato sauce, chicken broth, sugar, and black pepper to pot. Lock lid and cook for 1 (yes, one) minute at high pressure. Don’t worry, the soup will cook plenty as it comes up to pressure. Once cook time is complete, quick-release pressure.
Remove lid and add basil, parsley, and buttermilk. Mix well and serve.
You'll notice that (for once) there is no salt added to this recipe. There is salt in the butter, tomatoes, tomato sauce, and broth. No need to add anymore. But don't get used to me saying that. Lol.
It's a little unconventional to use buttermilk in this soup, but give it a try! It adds a unique tang that cannot otherwise be duplicated.
If at all possible, I recommend using homemade chicken broth. It will add a richness to this otherwise very light soup.