Take your puff pastry out of the freezer and let it warm up for about 45 minutes.
Make caramelized onions
While the pastry is warming, peel and slice 2 onions into long thin pieces and toss them into a frying pan with 2 tbsp of olive oil and a 1/4 tsp. salt. Cook the onions uncovered on low, stirring occasionally for 30-40 minutes until they turn a light brown color and get sweet. (Add a sprinkle of water to the onions as they are cooking if they start to look dry.)
Make mushroom "bacon"
Slice a large portabella mushroom into thin slices and fry in 1 tbsp of neutral-flavored oil. sprinkle with salt and liquid smoke and cook for about 7-8 minutes on each side until thoroughly cooked.
Make the tofu filling (or other fillings of choice)
Crumble drained, pressed, extra firm, or high protein tofu into a food processor and add vegan broth, poultry seasoning, nutritional yeast, soy sauce, salt, and pepper into a food processor and blend until combined.
(If not using the tofu method, use 12 oz. of vegan ground beef, or see further instructions in the variation section of this post.)
Assemble your wellington
Once you have prepped all of your ingredients be sure to preheat your oven to 400° F. (You need it to go into a preheated hot oven to get a great puffy rise!)
Place 1 rectangle of pastry puff on a cookie sheet that has edges.
Add a layer of caramelized onions down the center of the pastry puff leaving about 3 inches (7.5 cm) on both sides and about 1/2 inch (1.25 cm) on the top and bottom.
Layer the portabella mushroom bacon (or other vegan bacon if you choose) on top of the onions overlapping the slices of mushrooms a little.
Top with a layer of seasoned tofu (or vegan beef, lentil loaf mixture, or vegan meatball mixture) about 3 inches (7.5 cm) wide covering the onions and mushrooms, and about 1 1/2 inches (3.75 cm) high.
Cut diagonal lines in the puff pasty starting at the bottom corners at a 45-degree angle. Cut another line every inch until you reach 1/2 inch from the top.
Fold the top and the bottom triangles of the pastry in and on top of the filling. Then fold the strips over each other alternating each side starting at the top and working down to form a woven braided look.
Brush your wellington with a little melted vegan butter or aquafaba (the liquid from a can of chickpeas) to give it a little shine.
Bake the wellington at 400° F for 35 minutes or until the pastry has puffed up and become golden brown.
Allow cooling for about 10 minutes before slicing and serving.
Notes
Be sure to let your puff pastry warm up and soften before assembling your wellington.
You can layer onions, mushrooms, vegetables, tofu, or meat substitute of your choice, but don't fill it more than about 3 inches wide and 2 1/2 inches high.
Use a cookie sheet that has edges on the side. Some of the juices from the wellington will leak out and drip off the sheet without edges.
Variations
Vegan "Beef" Wellington - Use 12 oz. of a vegan beef substitute like Beyond Beef or Impossible Burger. The 12 oz packages that come unformed are perfect for this, but you can also use 6 pre-formed hamburgers, let them thaw, and roll them into a cylinder shape. (Don't use the frozen crumbles, they will not stick together as well to form your "meat.") You can also make your own beef wellington filling by making my meaty vegan meatball recipe and rolling the whole batch into a cylinder shape.Lentil Wellington - For a soy-free, plant-based wellington, a lentil mixture is a great option. Simply cut my lentil loaf recipe in half and use it as the meaty layer in your wellington. The lentils and rice in this are seasoned to perfection and will give you a great texture when baked.Mushroom Wellington - Simply double the amount of caramelized onions cooking a total of 4 onions. Saute 3 sliced portabella mushrooms in 2 tbsps of olive oil and sprinkled with salt. Layer the onions followed by 3 layers of sliced portabella mushrooms.