Parents magazine

Ingredients 1 sheet frozen puff pastry, thawed Reserved roast beef, thawed (about 1 lb.) 12 ounces frozen pearl onions 12 ounces frozen peas & carrots 2 tablespoons olive oil 12 ounces button mushrooms, sliced 1/2 teaspoon dried thyme, crushed 1/4 cup plus 2 Tbs. flour 2 1/4 cups unsalted beef stock 3/4 teaspoon salt 1 egg, beaten with 1 Tbs. water