Preheat the oven to 180C/350F. Combine the pumpkin with a drizzle of olive oil and a pinch of salt and pepper on a large baking tray. Slice the tip off a small bulb of garlic to expose the cloves. Drizzle with a dash of oil then wrap in foil and place in the middle of the tray.
Roast everything for 45mins, or until the pumpkin is fork tender and the garlic is super soft, golden and caramelized. They should roast at similar rates, but carry on roasting the garlic if it needs a little longer. With the same token, pull the pumpkin out early if it starts charring (a little colour is fine). Leave everything to cool for 5 mins.
Pop the pasta in well-salted water and cook until al dente.
Squeeze the roasted garlic into a food processor and blend until smooth with the pumpkin and around ⅓ cup / 80ml pasta water.
In a large pan over low heat, stir the cream, pumpkin puree, veg bouillon, nutmeg and ¼ tsp salt and pepper. Stir in the butter until it melts and blends into the sauce, then use tongs to transfer the cooked pasta straight from the pot into the pan, embracing any water that comes with it.
Toss to combine, then toss in the parmesan, using more leftover pasta water to thin out the sauce a splash at a time if needed. Check for seasoning and adjust if needed (ensure it's seasoned well to bring out the best in this simple sauce) then serve up and enjoy!