Grease a cast iron grill pan with olive oil. Heat it on a stovetop. Halve your tomatoes, onion, garlic (with skin), and pepper.
Arrange the tomatoes, onion, and whole garlic cloves (keep the peel on!) on a grill pan. Drizzle olive, sprinkle with salt, pepper, and thyme sprigs.
Grill the vegetables from both sides till the charred marks appear. Keep turning them at regular intervals for even roasting.
Once roasted, the tomatoes should be soft, slightly shriveled, and caramelized around the edges. The garlic cloves will be tender and mushy inside their skins. Remove the skin of tomatoes and garlic.
Transfer the vegetables to the blender (be careful—hot liquids expand!). Add vegetable stock. Secure the lid. Blend until silky smooth.
Transfer the tomato soup to a pot.Stir in the heavy cream (if using), chopped basl, and taste. Adjust the salt, pepper, and sugar as needed. Simmer the soup for 10 minutes to let the flavours meld.
Roasted Tomato Soup is ready to serve.