1) Puree the tomatoes, celery and stock in a blender until smooth. Season, to taste, with salt and pepper. Season with lemon juice and maple syrup. Stir in cream.
2) Transfer to a microwave safe bowl. Heat in microwave on high until warmed through, about four minutes. (Alternatively heat the old-fashioned way in a pan.)
3) Pour hot soup into an air-tight thermos. Pack in a lunch sack and send off to school.