Cook potatoes until tender; drain. Mash potato until smooth and stir in the milk and half the PHILADELPHIA cream cheese. Keep warm.
Heat butter in a pan and saute the onion and carrot until tender. Stir in remaining PHILADELPHIA cream cheese, mustards and the combined extra milk and cornflour. Heat, stirring, until smooth. Add the fish, peas and parsley, bring to boil then remove from heat.
Spoon mixture into 4 individual baking dishes or one larger one, then top with mashed potato.
Bake at 180 °C for 15 minutes for the individual or 25 minutes for the larger, until heated through and golden on top. Serve immediately.