Traditional Northumberland skillet classic: layered thinly sliced potatoes, sweet onions, and mature Cheddar cheese, cooked slowly in butter until crispy on the base and grilled until bubbling.
In a heavy ovenproof frying pan, heat oil and half the butter. Arrange overlapping layers of sliced potatoes, onions, and cheese, seasoning each layer with salt and pepper.
Dot remaining butter on top. Cover pan with foil and cook over medium-low heat for 20-25 minutes until potatoes are completely tender when tested with a knife.
Remove foil and increase heat for 4 minutes to create a crisp, golden-brown crust on the bottom.
Scatter extra grated cheese on top and place under a hot grill for 5 minutes until bubbly and golden. Cut into wedges.