In a large saucepan, heat the oil and sauté the onions and garlic for 3 to 5 minutes, or until the onions are translucent.
Stir in the thyme, tomatoes, and chicken stock and bring to a boil.
Reduce heat to simmer and cook for 30 minutes.
Remove the thyme sprigs.
In a blender or food processor, puree the soup, in batches, and strain out the tomato skins.
Return the soup to the saucepan. Mix in the cream and yogurt and bring to a boil.
Remove from heat and add the salt and pepper. Serve immediately.
