Preheat your oven to 200°C (390°F).
Peel and chop the root vegetables into small, uniform pieces. Spread them on a baking sheet and roast for about 25 minutes until tender and caramelized, filling your kitchen with a sweet, earthy aroma.
Meanwhile, finely chop the mushrooms or pulse them in a food processor until they resemble coarse crumbs. Sauté the mushrooms in a skillet over medium heat until they release their moisture and become fragrant, about 8-10 minutes.
Add minced garlic, chopped thyme, and a splash of balsamic vinegar to the mushrooms. Continue cooking until everything is well combined and the mixture is slightly thickened, about 5 minutes. Remove from heat and let cool.
On a lightly floured surface, roll out the puff pastry into a rectangle large enough to enclose the filling. Spread the cooled mushroom duxelles in the center, leaving space around the edges.
Pile the roasted root vegetables on top of the mushroom duxelles, spreading them evenly. Carefully fold the pastry over the filling, sealing the edges by pinching or pressing with a fork.
Transfer the assembled Wellington onto a baking sheet lined with parchment paper. Brush the top with beaten egg or plant-based wash for a shiny, golden finish.
Bake in the preheated oven for 35-40 minutes until the pastry is crisp and golden brown, and the filling is bubbling inside.
Once out of the oven, let the Wellington rest for 10 minutes to allow the filling to set. Slice carefully using a serrated knife to serve clean, beautiful pieces.
Enjoy this festive dish with your favorite holiday sides, celebrating the cozy, flaky, and flavorful layers of this veggie Wellington.
