Preheat the oven to 200°C/fan 180°C/Gas mark 6. Cut the marrow into thick slices and scoop out the middle of the marrow, leaving a little in the bottom to form a base. Drizzle a baking dish with a little oil, arrange the marrow in the dish and roast for 30 mins.

Meanwhile for the filling, heat 1 tbsp oil in a pan and sizzle the bacon/pancetta for 5 minutes, until just starting to crisp. Then add the finely chopped onion to the pan and cook for a further few minutes to soften.

Next add the mushrooms and thyme and cook for a further couple of minutes. Add the vinegar, sizzle for a moment then tip in the tomatoes and sugar. Add a splash of water to the tomato can to wash out every last bit and tip into the sauce. Season with chilli flakes and a pinch of salt and simmer until rich and thick.

Once the marrow in the oven has roasted for 30 minutes, lift out the oven and spoon the thick sauce into the middle of each marrow slice. Cover with foil and bake for 30 minutes.

After 30 minutes remove the foil, scatter over the grated mozzarella and return to the oven for 10 minutes until the cheese has melted.