Preheat oven to 200°C/180°C fan-forced. Place potatoes in a medium saucepan and cover with cold water. Season with salt and bring to the boil over high heat. Boil for 15 minutes or until tender. Drain.
Return potatoes to pan and cook over low heat for 30 seconds or until dry. Remove from heat.
Using a potato masher, coarsely mash potatoes and add milk. Mash until smooth.
Add 1/2 cup cheese and stir until smooth. Season with salt and pepper.
Place beans in a 5 cup-capacity baking dish. Cover with mash and sprinkle with remaining cheese.
Bake for 20 to 25 minutes or until golden and hot.