Heat broiler. Slice tomatoes in half and squeeze out juice and seeds; place skin side up in a jellyroll pan. Broil 10 minutes, or until skins blister and blacken. Remove from oven and allow to cool slightly. Slip off skins and discard. Puree in blender or food processor.
In kettle, heat oil over medium heat; saute onions until tender, then sprinkle evenly with flour. Stir with a wire whisk and cook 1 minute longer. Stir in tomato puree and broth; cook, stirring frequently, until mixture comes to a boil. Add roasted garlic, thyme, white pepper and salt and sugar; simmer
10 to 20 minutes. Turn off heat and stir in reserved milk.