Preheat the oven to 230c. Find a baking dish about 30 x 20cm or similar. Cut the pumpkin in half and scrape out the seeds and fibres. Put this in a saucepan with the water, garlic and sage. Microwave the rest of the squash for 2 minutes - this will help you peel it - and remove the skin. Add this to the saucepan and bring to the boil - this technique creates a flavourful, beautifully orange stock from what would have ordinarily been thrown away. Reduce to a simmer and cook for about 20 minutes.

While the stock is simmering, slice the pumpkin on the mandoline and set aside. When the stock is ready, strain it into another container to remove the squash remnants and sage - press them in the strainer to extract maximum flavour - and return to the saucepan. Add the homemade stock paste, if using, the cream, nutmeg and salt and pepper. Taste the stock - it should be flavourful and fairly salty as it will need to season both the potatoes and pumpkin in while it bakes. When you are happy with it, pour a little into the bottom of a baking dish to prevent the vegetables sticking, and keep the rest of it hot.

Cut the potatoes (doing this at the last minute stops them browning). Start layering the potatoes and pumpkin, alternating, keeping the vegetables overlapping but fairly loose so the liquid will be able to penetrate. When you have finished layering, pour over the rest of the liquid making sure there is still about 1cm left at the top to allow for bubbling up. Cover with foil and put in the oven.

Cook for about 30 minutes, to bring the cream/stock up to a gentle boil in the dish, then turn the oven down to 180c and cook gently until a knife poked through the vegetables reveals them to soft and thoroughly cooked - about two hours. Take it out of the oven, sprinkle with the cheese and herbs and grind on an generous helping of black pepper. Return to the oven for about 10 minutes until melted and toasty. Rest for about 10 minutes, then serve.