Chop the fresh tomatoes in half and toss them with minced garlic, olive oil, salt, and pepper until well coated.
Spread the seasoned tomatoes evenly in the bottom of the crockpot, making sure they are not stacked too tightly.
Cover the crockpot with the lid and set it to low heat. Let the tomatoes slow roast for about 6 hours, until they are deeply caramelized and fragrant, filling your kitchen with a smoky aroma.
Once finished, open the lid and use a ladle to carefully transfer the roasted tomatoes into a blender or food processor.
Add vegetable broth to the blender, then blend until smooth and velvety, about 30 seconds. Adjust the thickness with more broth if needed.
Pour the pureed soup back into the crockpot or a saucepan and warm gently over low heat for 10 minutes, allowing the flavors to meld together.
Taste and adjust the seasoning with more salt or pepper if desired. Serve the soup hot, garnished with fresh basil or a drizzle of olive oil if you like.