Melt ¼ cup (½ stick) of butter in a large saucepan and add the olive oil. Add the onion, thyme, basil, salt and pepper and cook, stirring occasionally, until the onion is wilted. Add the tomatoes and tomato paste and stir to blend. Simmer 10 minutes.
Place the flour in a small mixing bowl and add 5 tablespoons of broth, stirring to blend. Combine the flour mixture with the tomato mixture. Add the remaining broth and simmer 30 minutes, stirring frequently to prevent scorching.
Puree the soup in a food processor or blender, then return to heat and add the sugar and cream. Simmer, stirring occasionally, 5 minutes. Swirl in the remaining ¼ cup (½ stick) butter.
Serve hot, garnished with croutons- if desired.
Notes
*If you don't have fresh thyme and basil on hand, substitute 1 teaspoon dried for each
*If you don't want to use fresh tomatoes, substitute one (35-ounce) can of tomatoes, with liquid