Step 1

Set the frozen puff pastry out to thaw while you prepare the filling. It will take about 30 minutes to thaw.

Step 2

Preheat the oven to 375 degrees F and lightly grease a baking pan.

Step 3

Add the mushrooms to a food processor and pulse several times until crumbly, but be careful not to over process them. Alternatively, chop them small with a large knife.

Step 4

Warm the olive oil in a large pan over medium heat. Add the sliced onions and cook for about 30 minutes, stirring every few minutes, until caramelized. They should be golden brown in color. I like to season them with a little salt towards to end, around 1/4-1/2 teaspoon.

Step 5

Add the chopped mushrooms, garlic and soy sauce and cook for about 10 minutes, until the mushrooms have softened and the liquid released from the mushrooms has mostly evaporated.

Step 6

Add the thyme, rosemary and baby spinach. Stir well to combine as the spinach wilts. Remove from heat. You can add a little salt to taste, but I don't find this necessary (the soy sauce adds saltiness).

Step 7

Once the puff pastry has thawed, roll it out to about 9x12 inches on a piece of parchment paper (this will make it easier to turn over onto the pan).

Step 8

Add a layer of thinly sliced sweet potatoes to the middle third of the pastry. Top with half of the mushroom mixture, then add another layer of sweet potatoes. Add the rest of the mushroom mixture, then finish with a final layer of sweet potatoes. (see photos above in post for reference)

Step 9

Fold the sides of the pastry over the top of the mixture and pinch and seal the edges. Use a little water on your fingers to help it seal if needed.

Step 10

Carefully roll the wellington over onto the pan, using the parchment paper to help, so the seam side is down.

Step 11

Use a sharp knife to score the dough in a criss cross pattern.

Step 12

In a small bowl, stir the olive oil and milk to combine, then brush the tops and sides of the wellington with it.

Step 13

Bake for 40-45 minutes, until golden brown and puffy. Let it rest for 10 minutes before slicing. Serve with vegan gravy and enjoy!