Preheat the oven to 450.
Cut tomatoes in half or smaller if they are very large. Cut onions into large pieces. Peel garlic cloves.
Place all the veggies on a baking sheet then drizzle generously with olive oil. Sprinkle generously again with salt, pepper, then toss everything together gently to get it all covered. Roast for 30 minutes.
When the veggies are done roasting, pour everything, including the juices and basil in a blender and blend until smooth. Pour into a large pot You can also place in a large pot and use an immersion blender. Keep the heat at low/medium. Add the stock and cream, stir. Adjsut seasoning and add more salt if needed.
While the vegetables are roasting, you can make the grilled cheese. Take the butter and mash it with the garlic, parsley, and a pinch of salt. Spread over each slice. I also take a little extra butter and spread on the side that doesn't have garlic. I like to toast both slices for grilled cheese. It makes it so much better.
If you've toasted both sides, turn the heat a little lower than medium. Place one slice down, later cheese, then top with another. Use a spatula to gently press the bread down to melt the cheese. If you are making more sandwhiches, place the cooked ones in the oven on 100 F to keep warm. Serve with a bowl of soup and enjoy.