Vegan Mushroom Wellington

Day 1: Make Filling

Clean portobello mushrooms with a damp paper towel. Remove the stems and trim the edges to flatten them. Coat both sides of the portobello caps with 3 tablespoons of olive oil, then season with salt and pepper. In a large nonstick skillet, heat 2 tablespoons of olive oil over medium-high and cook the mushrooms gill-side down for 5 minutes. Flip and cook for another 5 minutes. Let them cool on a wire rack with the gill-side down.

Clean mixed wild mushrooms and roughly chop, about 1/4 to 1/2 inch. If using a food processor, work in batches to pulse the mixed wild mushrooms into small pieces. Place pieces in a large bowl. Mix in shallots, garlic, rosemary and thyme.

In a large nonstick skillet, heat 1/4 cup of olive oil on medium-high. When oil is hot, add half the wild mushroom mixture. Cook mushrooms stirring occasionally until caramelized, about 10 minutes. Transfer cooked mushrooms to a bowl and repeat the process with the second half of mushrooms. When the second batch is cooked, add the first batch back into the pan and add balsamic vinegar and soy sauce, and season with salt and pepper. Cook for 3 to 4 minutes until liquid has evaporated, then stir in walnuts, parsley and chives. Transfer the wild mushroom mixture to a sheet pan. Let cool to room temperature and then cover and chill overnight in the fridge.

Wipe skillet and return to medium-high heat with 3 tablespoons of olive oil. When oil is hot, add sliced onions. Cook onions stirring occasionally until lightly caramelized, about 5 minutes. Season with salt and pepper and stir in sherry vinegar. Cook stirring occasionally until liquid evaporates, about 5 minutes. Transfer onions to a small bowl, allow to cool to room temperature, and chill overnight in the refrigerator.

Day 2: Assemble and Bake

Preheat the oven to 400° F. Mix melted vegan butter and oat milk in a small bowl to make a wash.

Place a large piece of parchment paper on your work surface and sprinkle it with a little flour. Put the thawed puff pastry on the parchment. Using a rolling pin dusted with flour, roll out puff pastry into a 13-by-16-inch rectangle. Move the parchment and pastry to a large baking sheet, positioning it so the 16-inch side faces you. In the center of the pastry, spread half of the cooked mushroom mixture in a 4-by-10-inch strip, leaving a 1 1/2-inch border on both ends. Layer the caramelized onions over the mushroom mixture in a 3-inch-wide strip. Place the portobello caps on top, gill-side down, trimming if necessary. Add the rest of the mushroom mixture on top of the portobello caps and press it down to form an even layer, shaping it into a loaf.

Lift one side of the puff pastry over the filling, almost covering it completely. Brush the top of the folded pastry the wash. Lift the other side of the pastry, stretching it gently if necessary, and lay it over the wash brushed part to form a second layer. Press down lightly to seal the two layers together. Brush the wash on the inner edges of the ends of the pastry. Press the top and bottom of each end together and tuck them underneath to seal. Trim any excess parchment paper so that it fits on the baking sheet.

Brush the remaining wash over the top of the exposed puff pastry. Decorate the top as desired. Gently slice crisscrosses into only the top layer of the pastry, be careful not to pierce the second layer. Bake in the oven until golden brown and flaky, about 45 to 50 minutes. Remove from oven and allow to cool slightly on the baking sheet, about 10 minutes, before serving.