Slice tomatoes in half and place on a baking tray. Drizzle with 2-3 Tbs of olive oil and season with salt and pepper. Toss to coat evenly; turn all tomatoes cut-side up.
Peel onion and slice into 1/4 inch thick discs. Peel garlic cloves and leave whole. Place onion and garlic on separate baking tray; toss with salt, pepper, and olive oil as before.
Place both trays in oven. Roast onions 30 minutes and tomatoes 40 minutes.
Remove any pieces of vegetables that look too crispy and remove the tomato peels.
Add all roasted veggies to a large pot. Add 3 cups vegetable broth and basil.
Bring to a boil; reduce to simmer for 20 minutes.
If desired, add stick of butter and heavy cream; stir to incorporate.
Blend soup with an immersion blender or in small batches in a blender (with center removed from blender lid to let steam vent). Add remaining vegetable broth for a thinner consistency if desired (I’m usually happy without the extra broth).
Garnish with some fresh basil if you feelin’ fancy 😉
Enjoy! (Keeps well in fridge for 3-4 days)