Rinse, trim, and thinly slice the celery. Peel the garlic, finely chop, mix with a little salt, and crush with the back of a knife into a paste. Blanch the tomatoes in boiling water and remove. Peel, quarter, remove the core, and dice small.
Sauté the celery with garlic in the olive oil briefly. Add the tomato paste, then deglaze with the vegetable broth. Add the tomatoes and simmer over low heat for 5 minutes. Season with the sugar, lemon zest, salt, and pepper. Garnish with the chopped parsley.