1
Preheat the oven to 375°F.
2
Line a baking sheet with parchment paper.
3
Thaw puff pastry on the counter.
4
Add half of the mushrooms to a food processor and pulse 10 to 15 times until crumbly, then transfer to a bowl.
5
Add the remaining mushrooms to the food processor and process similarly.
6
Heat a couple tablespoons of avocado or olive oil in a skillet over medium-high heat.
7
Add the red onion and sauté for 3-4 minutes until lightly browned.
8
Lower the heat to medium and add minced garlic, stirring for 1-2 minutes until slightly soft.
9
Add the mushrooms and 2 tablespoons of balsamic vinegar, cooking for 10-12 minutes until most liquid evaporates.
10
Chop fresh sage and thyme, and roughly chop spinach.
11
Add another tablespoon of oil to the skillet, then add chopped herbs and water chestnuts, sautéing for about a minute until fragrant.
12
Season with 3/4 teaspoon salt and 1/4 teaspoon pepper, then add spinach and stir until wilted.
13
Combine all filling ingredients in the skillet and check seasoning.
14
Let the filling cool, then lightly flour the work surface.
15
Roll out the puff pastry to extend about an inch or two in every direction.
16
Transfer the puff pastry to the lined baking sheet and form a loaf shape with the filling in the center.
17
Pinch the long ends of the pastry together, leaving the ends loose.
18
Slice off about an inch from each end of the pastry, twist these pieces together, and place them on top of the Wellington.
19
Create 1-inch slits on either side of the Wellington with a sharp knife.
