1 large onion
1kg floury potatoes, such as King Edward, cut into 5-6 mm slices
225g hard cheese such as mature cheddar, coarsely grated
In a frying pan, melt 50g of the butter. Add the sliced onions, season well. Cook gently until soft and lightly browned.
Pre heat oven to 200C/fan 180C/ Gas 6. Bring a large pan salted water to the boil. Add potatoes, return to the boil 4-5 minutes until just tender. Drain well and set aside.
Heat remaining butter in a large non-stick ovenproof frying pan. Arrange about1/3 of the potatoes in the pan and fry gently for about 5 minutes until crisp and golden underneath. Remove from the heat, cover with half the cooked onion, a little seasoning and a third of the cheese. Add a second layer of potatoes and the remaining onion. Season then scatter over half the remaining cheese. Add a final layer of potatoes, then scatter with the remaining cheese
Transfer the pan to the oven and bake for 25-30 minutes until golden
Substitute corned beef (and bacon if desired) for the cheese
Pour beef gravy mixed with beef stock over the top before putting in the oven
If desired, finish by crisping the top under the grill.