Potato Pot Pie with Rosemary

• 2lb potatoes
• 1lb onions
• salt and pepper

Peel the potatoes and onions and slice them thinly. Put into a greased casserole in alternate layers, seasoning well with salt and pepper and with very finely-chopped rosemary leaves. Dot with the butter and finish with a layer of potatoes. Pour in the milk. Put on a lid and bake at 350°F, 180°C, gas mark 4 for one and a half hours until the milk has been absorbed. The lid should be removed for