Roughly chop the chestnuts. Put a large, deep frying pan or wok on a medium heat for 2 mins, then add the chestnuts. Toast them for 2-3 mins, shaking the pan every so often, till the chestnuts are browned and smell nutty. Tip out into a bowl and set aside.
Halve the butternut squash and scoop out the seeds. Peel and chop it into chunks around 1cm across. Put the frying pan back on a medium heat and add ½ tbsp oil with the squash. Pop a lid on the pan (or use a baking tray if you don’t have a lid) and cook the squash for 8-10 mins, stirring every so often, till the squash has softened and has started to brown and caramelise.
While the squash cooks, put a large pan of salted water on to boil. Thickly slice the mushrooms. Finely chop the rosemary leaves.
Add the mushrooms to the squash with a pinch of salt and pepper. Fry, stirring every so often and without the lid, for 5 mins till the mushrooms start to look juicy.
The water in the pan should be boiling by now, so add the gnocchi to the pan and simmer for 3-4 mins till the gnocchi start to rise to the surface. Drain them well.
Tip the drained gnocchi into the mushrooms and squash pan. Add the rosemary and chestnuts. Pour in the cream. Gently cook for 2-3 mins, stirring often, till the cream is warmed through and thickened slightly. Taste the sauce and add a pinch more salt and pepper if you think it needs it.
Toss the salad leaves with 1 tbsp balsamic vinegar. Spoon the gnocchi onto warm plates and serve with the salad on the side.