Vegetarian Mushroom Wellington Recipe

Ingredients

• 4 large portobello mushrooms, each about 3 inches wide (8 to 10 ounces total)
• ½ cup plus 5 tablespoons olive oil
• Kosher salt
• black pepper
• 2 pounds mixed mushrooms, such as shiitake, oyster and cremini
• Ice, for cooling
• 4 shallots, finely chopped (about 1 packed cup)
• 6 garlic cloves, finely chopped
• 2 tablespoons finely chopped fresh rosemary
• ⅓ cup port, or 1 to 2 tablespoons good-quality aged balsamic vinegar
• 2 tablespoons soy sauce
• 1 tablespoon fresh thyme leaves
• 1 cup finely chopped toasted walnuts (about 4 ounces)
• 3 tablespoons unsalted butter
• 2 small yellow onions, cut into ¼-inch rounds
• ¾ teaspoon light or dark brown sugar
• 1¼ teaspoons kosher salt
• ¾ teaspoon black pepper
• 1 cup apple cider or apple juice
• 1 tablespoon good-quality aged balsamic vinegar (optional)
• All-purpose flour, for dusting
• 1 (14-ounce) package puff pastry
• 1 large egg, beaten