Quarter and seed the red peppers. Core and cut the tomatoes in half lengthwise. Place peppers and tomatoes, cut side up, on a foil-lined baking sheet. Add garlic and onion. Mix oil with salt, thyme, rosemary, basil and pepper. Brush over vegetables. Roast on the bottom rack of a 450 F oven for 50-60 minutes or until tender and slightly charred. Let cool for 30 minutes. Slip skins off tomatoes.
In batches, in a blender or food processor, puree vegetables and any juices, along with chicken stock until smooth. Return to sauce pan and add any remaining chicken stock. When soup has heated, garnish with a swirl of sour cream and fresh herbs. Serve immediately.