Start by cooking the pumpkin or squash. Heat oven to 180C/160C fan/gas 4. Put the pumpkin in a large, deep roasting tin. Add a splash of water, no more than
a few tbsps, then cover with foil. Make a small steam hole in the middle, put in the oven and cook for 45 mins or until very tender. While the pumpkin cooks, tip the seeds for the crust onto a baking tray and put in the oven on a lower shelf for 10 mins until toasted and starting to pop, then cool. Once cooked, tip the pumpkin into a sieve, drain and cool completely.
Meanwhile, prepare the crust. Tip the toasted seeds and biscuits into a food processor and blitz to fine crumbs. Add the stem ginger and melted butter, and blitz again until the mixture is like wet sand. Tip into a 23cm fluted, loose- bottomed tart tin or a pie tin. Use the back of a spoon to spread the mixture evenly over the base and up the sides of the tin, pressing it firmly into place. Make sure there are no holes, so the filling can’t escape. Put in the fridge and chill for 30 mins. Clean the food processor.
Turn oven down to 160C/140C fan/ gas 3. When the pumpkin is cool and any excess liquid has drained away, tip into the food processor. Add the remaining ingredients for the filling and blend until smooth. Put the chilled crust on a baking tray in the middle of the oven. Pull out the shelf and carefully fill with the pumpkin mixture, pouring it right to the top. Close the oven and bake for 40 mins – the filling should be set but still have a wobble. Cool in the tin to room temperature, then chill for at least 1 hr.
For the brittle, put the pumpkin seeds in a large heavy-based frying pan and toast for a few mins until golden and starting to pop. While they toast, line a baking sheet with baking parchment. Tip the seeds into a bowl and set aside, then wipe out the pan. Tip the sugar into the pan and set over a medium heat. To turn the sugar into caramel, heat until the sugar dissolves, but don’t stir at any stage or it may crystallise – instead, swirl the pan every 10 secs or so. Increase the heat and bubble the liquid sugar until it reaches a deep caramel colour. Quickly add the seeds, swirl to incorporate, then tip out onto your lined tray. Leave to cool and set for 30 mins.
Just before you’re ready to serve, prepare the cream. Pour the cream and syrup into a large bowl, and whisk until softly whipped and billowy. Remove the pie from the fridge and from its case, and place on a pretty plate or cake stand, or serve straight from the tin. Pile the cream onto the centre of the pie and swirl towards the edges, leaving a border of pumpkin exposed around the edge. When the pumpkin caramel is set, break it into small pieces with a rolling pin and sprinkle over the top – if you have more than you need, store the remainder in a sealed container for up to 2 weeks to scatter over ice cream. Serve the pie in wedges. Leftovers will keep in the fridge for up to 3 days.