Cut the spaghetti squash in half lengthwise with the cut surfaces facing up in a baking tray, season with salt, place in the middle of the oven heated to 180 °C, pour about 8 dl of water into the baking tray, cook for about
cook for about thirty minutes.
Take out, cool slightly, loosen the flesh with a fork.
In the meantime, cook the hazelnut sauce: Warm butter in a frying pan. Saute flour until soft, stirring with a whisk over medium heat; flour should not take on color. Remove frying pan from heat, pour in milk and cream all at once, stirring to bring to a boil, reduce heat, season with salt, a little pepper and a little nutmeg, simmer gently at medium heat, stirring occasionally, for about ten minutes until sauce is creamy. Spoon test: The sauce has the right consistency when it coats the back of a spoon evenly. Add hazelnuts, spread sauce evenly into pumpkin halves.
For the hazelnut crumble, mix hazelnuts with cheese and butter in a small baking bowl with a fork until crumbly, spread evenly over the squash.
Bake au gratin: about twenty minutes in the middle of the oven heated to 200 degrees Celsius.