Preheat the oven to 400 degrees F. Arrange tomato halves onto a baking sheet. Drizzle with olive oil, then sprinkle with salt and black pepper. Roast tomatoes for 40-45 minutes. Or, air fry tomatoes at 450 degrees F for 15-20 minutes.
Meanwhile, place a dutch oven or large pot over medium-low heat. Add 1 tablespoon of oil and add the onion with a pinch of salt. Cook the onions for 30 minutes, stirring occasionally. Add a bit of water to the onions if they begin to stick.
Add 1 teaspoon of butter and add the crushed garlic to the dutch oven. Stir to combine and cook the garlic for 30 seconds.
Pour tomatoes and their juices into the dutch oven. Add vegetable stock and basil leaves. Simmer with a lid for 10 minutes.
Carefully transfer the contents in the dutch oven to the blender. Blend until smooth. Pour the soup back into the dutch oven and add sugar. Cover and simmer for 10 minutes.
Serve soup with chopped basil, salt, and pepper.
Use a high-powered blender to breakdown all of the ingredients into a smooth soup. I personally use an Oster blender. Take caution when blending the soup. It will be hot.
If you find your soup is too thin for your liking, simply simmer the soup for longer during the final cooking steps. Alternatively, if it’s too thick, add a bit more vegetable stock.