Boil water for the macaroni.
Chop the butternut into small cubes and fry in butter with sage.
For the cheese sauce:
Melt butter, and wait until it turns ever so slightly brown. Add milk, while stirring, until smooth.
Add half of the cheese into the sauce and stir until incorporated. Set aside.
For the mushrooms:
Fry the chopped red onion and leeks in butter and olive oil. Add bacon, then the mushrooms.
Chop and toast hazelnuts in a pan, with a little butter.
In a bowl, beat the eggs with the cream. Stir in mustard and paprika. Add a small amount of the cheese sauce to the eggs, while stirring, to make a custard.
Add the eggs back into the cheese sauce, stirring until smooth. Set aside.
Cook pasta according to package instructions.
Mix the butternut, some of the bacon and mushroom mixture (keeping some aside for garnish), and cheese sauce with the pasta. Season to taste.
Pour into an oven-proof dish. Top with remaining cheese and bake for 15 minutes at 200 degrees.
Garnish with the rest of the mushrooms, more grated Grana Padano and the toasted hazelnuts. Serve.
Click HERE to watch Reuben making this dish!