Cut red peppers in half lengthwise; pull out the seeds and membranes. Place cut side down on a baking sheet that has been lined with foil. Roast at 450°F or broil on high for about 30 minutes (less under the broiler), until blackened and blistered, rotating the sheet if necessary for them to cook evenly.
Remove from the sheet and place in a bowl; cover with the foil or a plate and let cool. When cool enough to handle, peel off the skins and discard them, dropping the peppers back into the bowl.
In a large saucepan or Dutch oven, heat a drizzle of oil over medium-high heat and sauté the onion for 5 minutes, or until soft. Add the garlic and cook for another minute, add the thyme, tomatoes and chicken stock and bring to a simmer; add the red peppers along with any juices that have accumulated in the bowl and cook for about 20 minutes.
Turn the heat down to low and add the cream, salt and pepper. Puree with a hand-held immersion blender or transfer to a blender in batches and pulse until smooth. Heat through, adjust the seasoning and serve warm. If you like, top each bowl with a small dollop of sour cream, and run a bamboo skewer through it to create a teardrop shape.