Melt butter over medium-low heat in a large saucepan. Add scallions and cook, stirring occasionally, about 4 minutes, or until scallions begin to soften. Stir in tomatoes, chicken broth, roasted peppers, basil, salt and pepper. Increase heat to high and bring mixture to a boil. Reduce heat and simmer, stirring occasionally, about 10 minutes. Remove saucepan from heat, stir in heavy cream and season to taste with salt and pepper. Serve hot.