First the galette crust: put the pistachios, sunflower or pumpkin seeds on a baking tray and roast in the hot oven alongside the squash for 5 minutes. Remove the tray of nuts and seeds (leaving the squash to carry on roasting) and tip them into a food processor with the chestnuts, olive oil, maple syrup, lemon zest, thyme and a good pinch of salt and pepper. Blitz until you have a fine crumbly paste that comes together when you squeeze it. If it is too crumbly, add a touch more oil until it comes together into a solid piece when you scrunch it in your hands. Lay a sheet of baking paper on your work surface, then tip out the paste and shape it into a circle with your hands. Place another sheet of baking paper on top and use a rolling pin to roll it out into a pizza-sized circle about 0.5cm thick. Put it on a baking tray and take off the top sheet of paper, then prick the dough with a fork and pop it into the oven alongside the squash for 15–20 minutes, until golden around the edges.ake it out and let it cool a little. If the squash is ready before the crust, take it out and set it aside.