Preheat oven to 410°F/220°C
Make the flax eggs: In a small bowl, mix together the 2tbs of ground flax with 5tbs water, set aside. Allow to sit for 10 minutes until it become a gel-like substance. Setting the bowl in the frige will allow them to gel up faster.
Prepare the meat mixture: In a medium-sized bowl, mix together the beyond beef, flax eggs, bread crumbs and 1tsp salt until well combined. Mixing it with your hands is the easiest. Set aside.
Heat 2tbs of olive oil in a large skillet over medium-high heat. Add the onion and cook for a few minutes until the onion starts to turn translucent. Add the garlic and cook for a few more minutes.
Add the mushrooms and cook for about 5 minutes until they release their liquid and start to brown. Add 1/4tsp salt
Add the wine and cook on a medium heat for about 5-10 minutes until almost all of it is absorbed into the mushrooms
Add the onion and mushroom mixture into the bowl with the meat mixture and mix with a spoon to combine.
On a baking sheet, lay out the puff pastrys horizontally with the paper underneath, overlapping by about 1.5 inches. Press gently with your fingers to ensure that they stick together.
Pour the meat mixture into the center of the puff pastries, and form it into a rectangular log shape with your hands. I like to make mine about 6 inches wide with the height of about 2 inches.
Fold the puff pastry over the meat mixture one side at a time. Try to stretch the second side over as far as possible to the other side.
Mix together the melted butter and soy milk and brush over the whole beef wellington.
Make the decoration. With the sharp end of a small knife, draw lines long-ways (horizontally) down the wellington about 1 inch apart. Then draw diagonal lines each way. See YouTube video for more detail.
Place into the preheated oven and allow to cook for 45-50 minutes until the top is golden brown but not burnt. Be sure to check the wellington at 30 minutes, and if it is getting too dark at the top lay a piece of parchment paper on the top to prevent burning.
Remove from the oven and allow to cool for 5-10minutes before cutting in slices. Enjoy!