Press the water out of the tofu. Drain the tofu and cut it into an 8 ounce block. Place it on a cutting board lined with paper towels. Place more paper towels on top of the tofu and weight them down with a few heavy cookbooks or a heavy skillet filled with a few cans of beans. Let sit for 30 minutes while you prepare the rest of the filling.
Cook the mushrooms. Heat the olive oil in a large frying pan over medium high heat. Add the onions with a tiny pinch of kosher salt and cook for 5 minutes, or until softened. Add the garlic, mushrooms, thyme, rosemary, paprika and black pepper. Cook until the mushrooms are softened and the liquid has evaporated, about 5 minutes. Then add the kosher salt and cook for one additional minute. Remove the mushrooms from the heat and allow to cool completely. You can speed this process up by transferring them to a bowl and placing in the fridge.
Toast and blend the walnuts. While the mushrooms are cooling, toast the walnuts (instructions are in the Recipe Notes). Allow to cool slightly. Transfer the toasted walnuts to a food processor and blitz until you have fine crumbs, but don’t overprocess or it will start to turn into walnut butter. Transfer the ground walnuts to a bowl.
Preheat the oven to 350°F / 175°C.
Make the mushroom-tofu filling. Add the cooled mushroom mixture to the food processor, along with the pressed tofu, miso paste, nutritional yeast, tomato paste, and lemon juice. Blend until you have a somewhat smooth, slightly sticky mixture that comes together.1. Add in the reserved ground walnuts, bread crumbs, and flour, and blend again until all of the ingredients are well incorporated.2. For a visual of what the consistency should look like, check out the photos in the blog post.3. If your filling is warm (this will be the case if you did not cool the cooked mushrooms), refrigerate it for 15-30 minutes until it is easy to mold together with your hands.
Line a baking sheet with parchment paper. Transfer the mushroom-tofu filling to the pan and use your hands to form it into a log shape that is roughly 7 inches or 18 cm long. See the photos in the blog post for reference.
Bake the filling. Bake the mushroom-tofu log for 30 minutes until it is relatively firm to the touch. Allow to cool completely.
Defrost the puff pastry and/or make the gravy. While the log is cooling, place some flour down on a flat work surface and lay the sheet of puff pastry down. Allow to thaw and come to room temperature, about 20-30 minutes. If you are making the gravy, you can get started on that.
Assemble the pastry. Once the puff pastry is thawed, use a rolling pin (or a chilled wine bottle) to roll the pastry into a rectangular shape that is roughly 9 inches wide x 13 inches long (23 cm wide vs. 33 cm wide).
Braid the dough (look at the photos in the blog post): Place the cooled mushroom log in the middle of the pastry sheet so that the top and bottom of the log almost touch the edges of the pastry, widthwise. Start on one end of the pastry and use a paring knife to cut 1 inch/2.5 cm strips about a fourth of the way up, almost but not quite reaching where the mushroom log is. Repeat on the other side. You should have about 9 strips on each side.1. Whisk together the plant-based milk and oil in a small bowl. This is the vegan “egg wash.” Use a pastry brush to brush the egg wash onto each strip of dough.2. Starting at one end, braid a pastry strip on top of the log, alternating each side. When you finish braiding the strips, pinch and tuck the in the edges into the top and bottom of the log, and brush on some of the egg wash to help seal the edges.3. Lightly prick the dough all over with a fork - the small holes will allow steam to escape during baking, making for more even baking. Brush the egg wash all over the rest of the pastry and then sprinkle with some coarse/flaky sea salt.
Refrigerate the pastry for 15-20 minutes to allow the dough to cool back down (baking the puff pastry while it’s warm may cause it to bake unevenly).
Preheat the oven to 375°F / 190°C and line a baking sheet with parchment paper. Remove the pastry from the fridge and bake for 25 minutes. Then increase the oven temperature to 425°F / 218°C and bake for another 10 minutes, or until the top is beautifully golden brown, flaky, and puffed.
Allow to cool for 10 minutes before slicing through. Serve plain or with the Mushroom Gravy.