Preheat the oven to 180°C (fan-forced) and line a baking tray. Leave the tray in the oven to preheat.
If using frozen puff pastry, remove it from the freezer and let it thaw on the kitchen counter.
To prepare the pumpkin, peel it and slice off its top and bottom, then cut it in half lengthwise. Scoop out the seeds from the bulbous part, then cut it off. You should now have four pieces of pumpkin, two small dome-like pieces (bulbous part) and two longer pieces that should look like two halves of a cylinder. Grab the two longer pieces and cut them again lengthwise so that the height of the ‘semi-circle' is about 3 cm. These pieces will be used whole for the centre of the wellington. Cut the other pieces into evenly sized large chunks.
Mix the olive oil and Bavarian Chicken Spice and using a pastry brush or your hands, massage into all the pumpkin pieces. Transfer them to the pre-heated baking tray and bake for 15 minutes.
Check the pumpkin again, the small pieces should be cooked and soft and can be removed from the oven. The larger pieces may need an extra 5-10 minutes. To check for doneness, insert a knife into the middle of the pumpkin, you should feel some resistance, but the knife should be able to go all the way through. Make sure to not overcook the pumpkin, otherwise it will be very difficult to work with when assembling the wellington. When the pumpkin is cooked, set aside to cool down.
Begin making the filling by chopping the shallots, garlic, and sage very finely. Add them to a hot, large frypan with the olive oil, Bavarian Chicken Spice and cook on low heat for 10 minutes, until the onions turn golden. Put the mushroom through a food processor and pulse a few times to turn them into breadcrumb-sized pieces. Add them to the pan and cook for another 10 minutes over medium heat.
In the meantime, add the macadamia nuts to a food processor and pulse until they turn into a coarse meal.
Add 1 tbsp balsamic vinegar and cook for another 5 minutes, stirring often. The mushrooms should be deeply brown and crumbly in texture, as the goal of this step is to evaporate most of the water from them.
Add the macadamia meal, breadcrumbs and dried cranberries and cook for another 3-4 minutes, careful not to burn the mixture. Finally, add the remaining 1 tbsp balsamic vinegar and all the roasted pumpkin pieces with the exception of the two large, rounded halves that will be used to fill the centre of the wellington.
Mash the pumpkin pieces well to incorporate with the mushroom mix, and cook for another 3-4 minutes until the paste sticks well together. Transfer to a bowl and let it cool for 10-15 minutes.
Prepare the pastry by lightly dusting a large baking mat. Slightly overlap the edges of the two sheets of pastry, then gently press them together with a rolling pin by a back-and-forth motion. This will create one long, rectangular pastry sheet. Roll out the shorter side by 3cm so that it can easily encase the pumpkin.
Spoon the mushroom mixture at the centre of the rectangle in the same width and length as the two roasted pumpkin pieces. This should be about 1cm thick. Place the pumpkin pieces over it, one after the other, to form one smooth log. Using your hands, pat the rest of the filling on the pumpkin pieces to fully encircle them.
Fold the pastry over the pumpkin so that it overlaps on top of it, trim the pastry excess and seal the trimmed edges very tight to avoid the pastry opening during baking. Use the excess pastry to patch up tears or for decoration. Cut the remaining sheet into strips and place them over the pastry casing in a criss cross style.
Carefully transfer the pumpkin to a baking tray (this should have been made easier by preparing the pumpkin directly on the baking mat).
In a small bowl, mix the maple syrup, olive oil and almond milk to make an ‘egg wash’. Brush the mixture all over the pastry.
Bake for 35-40 minutes or until the pastry is deeply golden and crispy. Serve immediately.