Start by preheating your oven to 400°F (200°C). While that’s heating up, slice the portobello mushrooms into small pieces. This will help them cook evenly and blend seamlessly into the filling.

In a large skillet, heat 2 tablespoons of olive oil over medium heat. Add the finely chopped onions and a pinch of salt. Sauté them until they are translucent and soft, about 5-7 minutes. This will provide a sweet base for our mixture.

Once the onions are ready, stir in the minced garlic and the chopped mushrooms. Cook for another 5 - 10 minutes until the mushrooms release their moisture and start to brown. Look for a rich color; this is where the flavor starts to develop!

Now it’s spinach time. Toss in the fresh baby spinach, mixing it well until it wilts, about 2-3 minutes. Season with pepper, thyme, and nutritional yeast. The nutritional yeast adds a cheesy, umami flavor without any dairy.

Once everything is well combined, remove the skillet from heat and let your filling cool. It’s important to do this to ensure your pastry doesn’t get soggy.

Dust your workspace with a little flour and roll out the vegan puff pastry. If you have a sheet that’s pre-rolled, you can skip this step. You’ll want a rectangle shape large enough to fold over the filling.

Once cooled, spread the filling in the center of the pastry, leaving space around the edges. Brush the edges with the aquafaba mixture. This will help seal your delicious creation.

Fold the pastry over the filling to create a package. Make sure to seal the edges well, using a fork to crimp the sides if desired. Give the whole thing a gentle brush with the remaining vegan egg wash.

Place the Wellington on a parchment-lined baking sheet. Bake in the preheated oven for 25-30 minutes or until golden brown. You will know it’s done when you can see a beautiful golden crust.

Once it’s out of the oven, let it rest for a few minutes. This allows the flavors to settle and makes it easier to slice. Serve it warm with your favorite sides.