Meatless Mushroom Wellington

Instructions

1. In a large skillet, heat two tablespoons oil over medium-low. Stir in baby bella mushrooms and yellow and green onions. Reduce heat to low; cook, stirring occasionally, until yellow onions are golden brown, about 25 minutes.
2. Increase heat to medium-high. Add apple juice, balsamic vinegar, garlic, soy sauce and thyme; cook, stirring occasionally, until liquid evaporates, 3–5 minutes. Stir in walnuts and spinach until spinach wilts, 1–2 minutes. Season with salt and pepper, if desired. Transfer to a bowl and refrigerate, uncovered.
3. In a large skillet, heat remaining oil over medium-high. Add portabellas top sides down; cook until lightly golden brown, about 5 minutes. Turn over; cook until golden brown, about 4 minutes more. Transfer stem sides down to a paper towel–lined plate and refrigerate, uncovered.
4. Preheat oven to 400 degrees. Lay a sheet of parchment paper on a work surface and dust with flour. Unfold puff pastry and, using a rolling pin, roll out into a 13x16-inch rectangle. Transfer parchment with pastry to a large sheet pan.
5. Spread half the vegetable-walnut mixture over pastry’s middle third, leaving a 3/4-inch border at top and bottom. Arrange portabellas, stem sides down, in a single line on top of vegetable-walnut mixture. Add remaining vegetable-walnut mixture on top and gently shape it and the portabellas into a loaf.
6. Carefully lift 1 side of pastry, fold it over filling and brush with beaten egg. Then fold right side of pastry to overlap the left side and press to seal, gently stretching as needed. Brush all over with remaining egg.
7. Bake until golden brown, 45–50 minutes. Remove from oven and let rest ten minutes. Serve sliced on a platter.