Vegetable potato top pie

Method

1. Preheat oven to 180°C.
2. Put potatoes in a saucepan half full with boiling water. Cook about 10 minutes, until tender. Drain and leave in saucepan to dry out a little. Mash with 1 Tbsp margarine and 2 Tbsp milk, then stir through wholegrain mustard.
3. Make a white sauce by melting 1 Tbsp margarine in the bottom of a saucepan. Add flour and stir to form a crumbly mixture. Add half the milk and mix continuously with a whisk or fork until there are no lumps and the sauce is starting to thicken. Add remaining milk and stir until it starts to thicken. Remove from heat and add Dijon mustard and cheese. 
4. Add chopped vegetables to white sauce and mix through. Place in the bottom of a baking dish. Top with mashed potato and bake for 30 minutes.