Heat the oven to 200C/180C fan/gas 6. Prick the potatoes all over with a fork, then rub the skins with the 2 tsp oil. Bake for 1-1 1/2 hrs until very tender when pressed and the skins are crisp.

While the potatoes are baking, make the ragu. Heat the olive oil over a medium heat in a large saucepan that has a lid. Fry the onion, celery and carrot with a pinch of salt for 10 mins until softened. Stir in the garlic and cook for a minute more. Add the mince, turn up the heat a little and fry the beef for 10 mins, breaking it up with a spoon, until browned.

Stir in the tomato purée, fry for a minute until darkened in colour, then add the wine, cook for a couple of minutes, and then add the bay. Simmer until reduced by half and pour in the can of tomatoes and the stock. Bring to a simmer, then turn the heat to low, cover with the lid and cook for 50 mins-1 hr until you have a rich ragu. Uncover for the last 20 mins to thicken the sauce if needed. Season well.

To make the béchamel, melt the butter in another saucepan over a medium heat. Sprinkle in the flour and mix well to create a thick paste. Cook the flour for 2 mins, then add the milk, a splash at a time, stirring continuously. Once all the milk has been incorporated, stir in the nutmeg and simmer for 3-4 mins until thickened enough to coat the back of a spoon. Season with salt and pepper.

Heat the oven to 220C/200C fan/gas 7. Split the jacket potatoes by cutting a cross into the tops and gently pressing the sides to create an opening. Transfer to a baking tray with a lip or a baking dish.

Divide half the mozzarella between the potatoes. Add a generous ladle of the ragu over the top, then a spoonful of the béchamel. Scatter over the remaining mozzarella, top with the parmesan and bake for 12 mins until the cheese melts and starts to turn golden.