Put the onions in a large saucepan and add the carrots. Sprinkle with the sugar, salt and pepper and pour in the stock – it will not cover the carrots, but they will cook in the steam. Cover the pan and bring to the boil, then reduce the heat and simmer for 5 minutes, or until the carrots are just tender.
Remove the lid from the pan and boil rapidly to reduce the stock by three-quarters. Add the peas and heat through. Stir in the cream and serve immediately.