Preheat oven to 220 °C/425 °F fan-forced. Line a large tray with parchment. Toss 800 g pumpkin cubes with 3 tbsp olive oil, 1 tsp salt, pepper. Spread in single layer. Roast 30–35 minutes until edges are dark caramelized (almost burnt in spots). This is non-negotiable.

While pumpkin roasts, toast hazelnuts at 180 °C/350 °F for 9–11 minutes until deep golden. Rub in clean towel to remove skins, chop roughly, set aside.

Heat your widest sauté pan over high. Add 60 g cold butter + 20 whole sage leaves. Cook 3–4 minutes until butter browns and sage crisps. Remove crispy sage to paper towel. Leave browned butter in pan.

In same pan, add ALL mushrooms. Cook undisturbed 6 minutes until deep golden underneath. Toss, cook another 5–6 minutes until liquid evaporates and they’re nutty. Season lightly, remove to plate.

Bring 6 quarts water to rolling boil. Salt aggressively.

In same pan (do not wipe!), add remaining 40 g butter + sliced garlic + 10 extra sage leaves for crisping. Cook gently 2 minutes. Remove crispy sage. Add roasted pumpkin + 250 ml cream. Simmer 3 minutes, then blend smooth with immersion blender (or regular blender). Return to low heat, add remaining 100 ml cream + nutmeg.

Drop penne into boiling water. Cook exactly 9 minutes (1 minute less than package).

Reserve 2½ cups pasta water. Using spider transfer penne directly into pumpkin sauce. Add ¾ cup pasta water + ALL cheeses in 4 stages while tossing vigorously OFF heat. Add more water until sauce is glossy velvet.

Return mushrooms to pan. Toss. Remove from heat, add final 2 tbsp cold butter cubes + half the hazelnuts. Rest 5 full minutes covered — sauce thickens to perfection.

Pile into warmed wide bowls, shower with remaining hazelnuts, crispy sage, extra Parmesan, cracked pepper, and optional truffle oil. Serve immediately with chilled Pinot Grigio and falling leaves.