For the pea citrus soup, prepare the vegetable soup and bring to a boil. Wash and clean the leeks and cut the white part into fine rings.
Heat the oil in a pot and sauté the leeks. Deglaze with vegetable soup. Add half of the peas and simmer for 5 minutes while stirring.
Grate lemon peel and squeeze lemon. Puree both with the rest of the peas and mint, add to soup and season with salt, pepper and sugar.
Stir in the corn, bring the pea-citrus soup to the boil again, season to taste and serve hot.