Cook the spinach without seasoning.
Meanwhile in a frying pan heat the oil and fry the carrot, onion and celery until golden. Then add the tomatoes (pulp them with a fork), the peas and some salt and cook gently for 15 minutes.
Strain the spinach and add the butter and fresh cream and cook for a further 10 minutes or until you have almost a thick purée. Put to one side.