Preheat the oven to 190C/170C fan/gas In a large oven dish add the squash tossed with olive oil, salt, garlic and sage and roast for 30 minutes until tender. Once tender mash the squash with the back of a fork.
In a pan of boiling salted water, cook the pasta following the pack instructions. Drain and set aside, reserving a splash of the pasta water to use later.
Stir half of the cheese in with the squash and gradually add the stock to create a smooth sauce, add some of the pasta water to loosen if needed before adding the pasta and coating well.
Top with the remaining grated cheese.
Turn up the oven to 200C/180C fan/gas 6 and bake for 20 Minutes until golden and bubbling.
In a frying pan heat a glug of Oil over a medium high heat, fry the brussel sprouts for 4-5 minutes until charred and tender. Top the pasta bake with the brussel sprouts to serve.