1. Slice your potatoes into 2 mm slices and toss in 2 tbsp vegetable oil. Lay out on a large baking tray and bake in the oven for about 30 mins, until tender and starting to crisp up a little. Set aside.
2. In a large wide saucepan, heat 2 tbsp oil on a medium heat. Add your onions and fry for a couple of mins, until just starting to soften. Turn your heat to high and add your beef mince, cooking for about 3 mins until starting to brown and crips up. Add the ketchup, mustard, onion powder, salt and pepper and stir to combine.
3. Grease a large springform cake tin and line it with parchment. Arrange your potato slices on the bottom of the dish and up the sides. Add a ladle of beef mix. Spread it out evenly, then top with bacon and cheese. Add another layer of potatoes, and continue until the tin is full and the potatoes reach the top. Finish off with parmesan, then bake for 1 hour until the potato is golden and totally tender when a skewer is inserted.
4. Serve & enjoy!