Cut the celery stalks and peeled carrots into sticks about 4 cm long and as thick as a match. Melt the butter, add the vegetables and cook covered for 15 to 20 minutes over a mild heat (add 1 dash of water if necessary). Put the cream and white wine in a pan and reduce until creamy over high heat, then season with mustard, sugar, salt and pepper. Mix the sauce carefully with the vegetables.