Step 1

In a medium saucepan, melt 2 tablespoons of the butter. Add the chopped onion, carrot, celery and garlic, cover and cook over moderately high heat, stirring occasionally, until the vegetables are just beginning to brown, about 5 minutes. Sprinkle the flour over the vegetables and stir over low heat for 1 minute, or until the flour is fully incorporated. Add the chicken stock, tomatoes, tomato paste and sugar and bring to a boil. Cover partially and cook the soup over moderate heat, stirring occasionally, until the vegetables are tender, 15 minutes.

Step 2

Transfer half of the soup to a blender and puree until smooth. Return the puree to the saucepan, add the heavy cream and cook until the soup is just heated through. Season the soup with salt and white pepper and swirl in the remaining 2 tablespoons of butter. Ladle the soup into bowls, garnish with croutons and serve.