Add all seeds and nuts into a small frying pan and toast them for 2 minutes over medium-high heat. Make sure to stir constantly so that they get toasted evenly and don't burn.
Use a blender or food processor to combine the toasted nuts and seeds with the vegetable fat and chestnut puree. Simply pulse until it's all combined, but don't blend it too smoothly - we still want some texture in the roast filling after all. (I actually used a stick blender when I mixed mine!)
Stir the almond flour into the nut mix until you get a sticky texture and set aside whilst you prepare the cranberry sauce.
Add the cranberries to a saucepan over medium heat and pour in about 30ml water to ease the heating process. Cook the cranberries until they start to steam, then start squashing them with the back of a fork. Stir regularly until the sauce thickens as the liquid evaporates. Add in the maple syrup (if using) and freshly squeezed orange juice and set aside.
Preheat your oven to 200 degrees, then wash & cut the butternut squash lengthwise in half hollow out the halves - this is where our filling will go.
Assemble the roast: Scoop the nut filling into one squash half, piling it up until you run out of the mixture. Spoon about half of the cranberry sauce on the top, leaving a little extra for serving later.
Add the second squash half on the top and use ovenproof ribbon to hold the parts together. I would also recommend poking 2 long toothpicks through the squash to keep it in place - most squashes can get a little slippery/uneven when heating and the picks will help the squash halves stay in place during the roasting process.
Place the squash on an ovenproof dish and roast in the middle of the oven for about 40-45 minutes - or until the squash is soft and golden. Carefully remove from the oven and slice (use a knife with saw tooth blade, that'll be easier).
Open a bottle of Appletiser and serve immediately with the roast - and don't forget to pour over the gravy (over the roast, not the drink, that is!).