For the ragu, heat 3 tbsp of the oil in a large saucepan over a medium heat and cook the onion, sage, bay, cinnamon and a large pinch of salt, covered, for 20 mins until the onions are soft. Meanwhile, heat the rest of the oil in a large frying pan over a medium heat and fry the pancetta for a few minutes until turning golden. Add the parsnip and fry for another 2 mins, then add the beef mince and brown all over, stirring occasionally. Tip the beef mixture into the pan with the onions. Add the tomatoes, cranberry sauce, stock and wine. Simmer for 1 hr 30 mins until the sauce is rich and has reduced slightly. Remove from the heat, discard the bay and cinnamon stick, and stir in the chocolate until it has melted.

While the ragu is simmering, make the chestnut sauce. Blitz 500ml of the milk with the chestnut purée or in a high-powered blender until smooth. Sieve into a large saucepan, then add the remaining milk and warm over a low heat until it’s just under a simmer. Melt the butter in a separate pan over a medium heat, then stir in the flour and cook for 2 mins until you have a paste. Slowly ladle the warm milk mixture into the pan, whisking continuously. Bring to the boil, whisking for 3-4 mins until thickened. Remove from the heat, season and stir in the parmesan and nutmeg.

Heat the oven to 180C/160C fan/gas 4. Spoon a little of the ragu into the base of a large, deep baking dish about 40 x 30cm (or if you don’t have a large enough dish, use two medium dishes). Top with a layer of lasagne sheets, making sure they don’t overlap, followed by a quarter of the chestnut sauce and a third of the ragu. Repeat twice more, then finish with a final layer of lasagne sheets and the remaining chestnut sauce. Sprinkle over the parmesan. At this stage, the lasagne can be wrapped and chilled for up to 24 hrs, or frozen for up to three months. Defrost in the fridge for 48 hrs before baking. Bake for 1 hr (or 1 hr 15 mins-1 hr 30 mins from chilled) until the sauce is bubbling and the top is golden and crisp.