In a large kettle, heat butter and olive oil over medium-high. Add onions and seasonings. Cook, stirring occasionally, until the onion is soft. Add the tomatoes and paste. Stir to blend. Simmer 10 minutes.
Place the flour in a small bowl and stir in 1/4 cup chicken broth. Stir into the tomato mixture. Add the remaining broth. Simmer 30 minutes, stirring frequently.
Allow mixture to cool and run through a sieve, food mill or food processor. Return the pureed mixture to the kettle. Add the sugar and cream. Heat through, stirring occasionally.
To prepare the croutons, rub the garlic over both sides of the bread. Brush with olive oil and place on a baking sheet. Bake at 350° for 10-12 minutes or until toasted. Turn and toast other side 2-3 minutes. Just before serving, top each bowl with one or two croutons.