1 package vegan puff pastry (thawed from frozen in the fridge - should be kept cold)
1/3 cup all-purpose flour, for rolling the pastry
Vegetable oil, to oil bread pan
Bring a pot of water to a boil and cook sweet potatoes until they are fork tender. Drain and set them aside.
Place all the ingredients for the apple cranberry sauce in a sauce pan and bring to a simmer. Stir occasionally, and once it's bubbling reduce heat to a low simmer and allow the sauce to reduce for approximately 20 minutes. It should be thick and darker. Set aside and allow to cool.
Meanwhile, mash the sweet potatoes in the pot you cooked them in and add the remaining ingredients. Stir and mash to combine well, set aside, and allow to cool.
To prepare the mushroom and lentil stew, heat a large pan over medium heat and add vegetable oil. Sauté onion, celery, and carrot together for 4-5 minutes until soft and mostly cooked through.
Add thyme, sage, nutmeg, sea salt, and ground black pepper and continue to stir for another minute or so. Then add in the mushrooms and cook for about 4-5 minutes until the mushrooms are mostly cooked through.
Add the garlic and lentils and combine well, stirring for 2-3 minutes.
Add the low-sodium vegetable stock and bring up to a simmer. Once simmering, combine the cornstarch and water in a small bowl, mix into a slurry and then add that to the stew. Stir over medium-low heat for 1-2 minutes until thickened and there isn't too much liquid remaining in the mixture. Turn off the heat and allow this mixture to cool down before adding to the pastry.
Preheat the oven to 375°F/190°C.
Sprinkle flour over your rolling surface, hands, and rolling pin before handling the pastry. Your puff pastry should unfold once into a rectangle shape. Roll this out to 1/8" thick and into a rectangle approximately 17" wide x 12" tall. You'll need to roll a bit, then flip the dough ensuring the rolling surface is floured to prevent the dough from sticking. Make sure to continually flour the rolling pin and your hands.
Make a cut about 3/4 of the way across. Cut from top to bottom (the shortest edge) so you have one large piece (approximately 11" wide x 12" tall) that will fit in a bread pan, and a smaller piece (approximately 6" wide x 12" tall) that will fit on top.
Cut a piece of parchment paper to fit in the width and longest sides of the bread pan with some overhang. Lightly oil the exposed narrower sides of the bread pan.
Gently place the largest piece of pastry into the bread pan, fitting it into the corners, and overlapping or folding any excess at the corners. Gently press it into all sides of the pan.
If you have any gaps, you can cut a small piece of the excess overhang from the side and use a small amount of water on a finger to glue the dough pieces together.
Layer the sweet potato mash on the bottom. It should be higher than an inch. Then add all of the mushroom lentil stew, and then all of the apple cranberry sauce.
Place the top piece of pastry across the top and gently press along the edge of the pan to seal it. Fold over the edges all the way around to form a crust. It can be rustic and uneven. Press the edges together with the prongs of a fork.
Using a sharp knife, cut 3 to 4 small slits along the top to allow steam to escape.
Bake for approximately 30 to 40 minutes on the middle rack. The pastry should be a dark golden color and the centre should be hot to the touch when you insert a knife or fork.
Once baked, allow it to rest for at least 20 minutes in the pan before lifting it out with the parchment paper.
If you want to prepare anything in advance, make all the fillings and refrigerate. Then roll out the pastry and assemble the whole roast right before baking for the best results.
A nice presentation idea is to use a piece of twine to tie the excess parchment around the roast. It helps with cutting as well and holding it together as you slice it.