Preheat oven to 200C. Place baking paper over a large baking tray.
Place pumpkin, onion and garlic on the tray – I find it easier to set the garlic cloves aside in their own area. Sprinkle over chopped rosemary then drizzle over grapeseed oil and rub into vegetables – season with freshly ground sea salt and pepper. Roast for 30-40 minutes, or until light golden brown and tender. Turn pan around half-way through if needed, to prevent burning. Remove vegetables from the oven and set aside.
Reduce oven temperature to 180C.
Meanwhile, while vegetables are roasting, cook pasta in boiling, salted water for 11 minutes, or until al dente. Drain, reserve a few tablespoonfuls of pasta water.
Squeeze cooked garlic out of skins. Place near the other roast vegies.
Add penne to a large, shallow, ceramic baking dish (mine is around 4cm high). Add walnuts, herbs, cheddar cheese and cream. Add a 3-4 tablespoons of pasta water and mix through until combined. Gently fold in vegetables until everything is combined- grind over black pepper. Scatter over parmesan evenly then drizzle over extra virgin olive oil.
Bake for 25 minutes, or until hot, creamy and bubbling. Scatter over more freshly chopped chives before serving if you like.