Cut bread into small pieces. Blanch tomatoes in boiling water for a few seconds, then rinse, peel, quarter, core and cut into cubes. Rinse, trim and cut celery into 1 cm thick (approximately 1/2-inch thick) slices. Rinse celery leaves and tear into small pieces. Set aside.
Peel and finely chop onion and garlic. In a pot, cook onion and garlic in hot oil until translucent. Add bread, tomatoes and celery and cook over high heat, stirring, about 1 minute. Add broth, bring to a boil, cover and simmer 5 minutes. Stir in creme fraiche and season with salt and pepper.
Divide soup among bowls and serve garnished with celery leaves.